Prototype 6.5 Grendel SAR Concept.

Hello, new member here.

I've been interested in the subject of firearms design and manufacturing for a long time now. I've always wanted to bring one or more of my designs from concept to working commercial model, but have always lacked the resources to do so, and that may never change. Regardlees, I've been seriously thinking about working on a 6.5 Grendel semi-automatic rifle design that, despite my limited resources, I might still be able to make a working prototype of, if I can keep it simple enough.

I was thinking of a tube gun based design, with the magazine well placed horizontally along the reciever, feeding just above the trigger/pistol grip assembly. Ejection would be straight down through a hollow pistol grip, as opposed to ejecting off to one side or the other, such as with the FG-42 or TRW LMR, both of which ejected to the right and about 3 inches closer to the operator's face than would otherwise be the case with a more traditional design. I had intended for the rifle to feed from the right with a short 20-30 round suomi/spectre type "coffin" magazine, in order to balance the weapon out a little better, and allow more rapid magazine changes by the right handed majority of us while still keeping the rifle butt tucked into our shoulders. Due to the nature of the design, with it's not easily accessible ejection port hidden up under and in the pistol grip, the design concept has been modified to a more "traditional" (for this type of rifle anyway) left hand feed, with a non-reciprocating bolt handle along the right side of the rifle that allows easier access to the bolt and chamber feedway in case of need during troublesome jams, and would also act as a usually closed dust cover for that jam service access port. I don't like having more than a rudimentary bolt handle arrangement on this rifle, and had preferred to place it on the underside of the rifle, but that may no longer be practical. Of course, for the sake of manufacturing and design simplicity, essential if I'm ever going to build a prototype model, the suomi/spectre "coffin" magazine idea is also out the window, at least for now. A 6.5 Grendel modified AR type magazine would be used instead. Not a problem.

The whole idea here is to eventually have a low cost U.S. built "poor man's" semi-automatic rifle commercially available to the U.S. civilian marketplace. One that is affordable to the common man (common men such as, well...poor guys like me), firing an inherently very good general purpose hunting/combat capable cartridge, in a reliable, detachable high magazine capacity, quick operating, user friendly, scope friendly, and accurate design. Which is why I'm looking at this rifle being a tube gun based type of design.

There are very few rifles currently available, or coming over the horizon anytime soon, that come anywhere close to fulfilling the above described rifle. If anything, just about everything coming down the pipe is even more expensive than what is already out there. Several are admittedly "cool", which doesn't mean much if you can't afford one. An SKS doesn't qualify. The various AK-47 and AK-74 clones out there are closer, but still don't qualify, as they are simply not inherently accurate enough, and aren't even all that cheap anymore these days. Even SKS rifles aren't all that cheap anymore, not like they used to be. If it was more accurate out of the box in it's base models, the Ruger Mini-14 series of rifles would be pretty close, but those are going up in price as well, and base models are clearly not anywhere near accurate enough. The Kel Tec SU-16 series of rifles is about as close as there is right now, but they are not as of yet available in a good enough cartridge. Perhaps they will be sometime in the near future. They still aren't really accurate enough. I am also personally uncertain of the long term durability and reliability of the SU-16 rifles. I had an AR-180B several years ago. If those were still being made, and in a more qualifying cartridge caliber, those might fit the bill. That one I had cost me only about $500 brand new, was definitely accurate, and fairly simple of design, though it's build quality was a little lacking...having had to be sent back to the manufacturer twice to get it to work right. It worked fine after that, but then had to be sold.

In order to keep my rifle design concept appropriately simple enough to build, and yet still meet the above outlined goals, while keeping it at or below a $500 retail price, it won't have a gas system at all. Instead, it will be a delayed blowback design. Roller locked delay blowback systems such as those used on the CETME and G-91 series rifles are way too mechanically complex and expensive to use for this low a price goal. The same goes for a design such as that used on the Johnson LMG, which had some reliability issues based on inherent weaknesses within it's design anyway, though I do still think it's a pretty cool system. I've considered, and am still considering, a highly simplified version of the basic concept used in the Johnson LMG, but I don't think it will be simple enough for me to make a good working prototype of at home, so that's out for now.

What I'm looking to do instead, is design a prototype rifle whose bolt locks up at the breach not too terribly unlike a more traditional gas tube operated based design, but which then unlocks and cycles by means of a fire group based mechanical time delay which cams the lock open after the bullet has left the barrel, but while there is still plenty of gas pressure energy left in the barrel to fully safely cycle the bolt. The idea is a little difficult to express, but I will do my best to better explain it in brief detail here. Keep in mind, this is all still mostly in my head at the moment, and not fully realized, so do please forgive me for any lapses on my part that make it difficult to picture what I'm trying to describe. Also, my use of firearm mechanism part nomenclature is not going to be all that precise, and I apologize strongly for that, but please try to follow with me on this anyway. Part of the idea here is to get some input from responses to this thread that will help me work out a better developed design of this lock work concept. I'm also greatly interested in any references to similar design ideas out there like this that I'm unaware of, and which might help point me in a better direction with conceptualizing the design. I'm also submitting this same basic thread over at the home gunsmith forum, hoping to get some valuable input from the active membership over there. It's a pretty cool site. If you have never been over there, you should check it out, especially if you are doing a home built 6.5 Grendel AR, or a home built firearm of any kind for that matter.

Imagine that this prototype concept rifle has two hammers. (The rifle is a hammer fired design at this point, due in part to understandable issues the BATF seems to have with tube guns...that can be perceived to be too readily converted to fire in full auto.) For our purposes here, one of these hammers will be referred to as hammer #1, which is the one that actually does the regular firing pin striking job of your typical fire group hammer. The other hammer will be referred to as hammer #2. Hammer #2 should probably be called something else, and eventually likely will be, but for lack of a better word we will stick with hammer #2 for now. The term hopefully works well for visualization purposes in this instance. After the rifle bolt has been fully cycled, either manually by the operator or after a round has been fired, hammers #1 and #2 have been reset to their near fully retracted positions, both waiting to be tripped the next time the operator squeezes the trigger. They rest nearly side by side when at rest, but not likely in exactly the same positions. They are also not likely the same size and shape, though for build purposes that would seem to be optimally desirable. Likely, hammer #2 is longer and heavier. Keep in mind that both, due to the layout of the rifle, will be located behind the trigger/pistol grip assembly, behind the operator's firing hand.

By practical necessity, when the trigger is squeezed, both hammers are released at the same time. Hammer #1 strikes the firing pin, which in turn sets off the round in the chamber. Hammer #2 is still rotating forward, passing where hammer#1 has struck the firing pin. It's all pretty much a matter of getting the preset timing right from here on out. If hammer #2 was moving to fast and engaging too soon, the bolt would unlock and open at an unsafe pressure level. Too late, the pressure level in the barrel would be too low, and the bolt wouldn't have sufficient energy imparted on it to properly cycle for the next shot. Just after the bullet leaves the barrel (assuming the timing has been worked out right, with enough of a window of opportunity to allow for a wide range of available bullet weights and powder loads to cycle properly for this caliber), hammer #2 then strikes a cam rod arm, which is under return spring pressure to keep it normally stationary when the bolt isn't cycling, or when it's not being hit by hammer #2. When struck by hammer #2, the cam rod arm kicks the locking arm (which, in at least this version of the design, looks and operates somewhat like an oversized extractor that wraps around one side of the barrel chamber) off of the barrel's fixed locking lugs (2 in this particular version), allowing the bolt to freely recoil backward. Another version of this setup, though not the one we're using in this example here, uses a tubular bolt carrier type of arrangement, in which the tubular bolt carrier has locking surfaces cut into it that lock onto matching lugs around the barrel breach, and this tube is what gets cammed unlocked by the cam rod arm described above, rather than a locking arm or claw. I'm still working on the tubular locking bolt carrier idea. It's not as fully developed as the locking arm/claw concept, but it looks as if it would be easier to construct, and operate in a bit more of a linear fashion.

In recoiling backward, the bolt (which doesn't have much of a bolt carrier at this stage of the design) recocks hammer #1 and hammer #2. Because hammer #2 is too long to recock like hammer #1 (the bolt would ride over it while hammer #2 was still forward, binding up the works), hammer #2 is recocked indirectly by a fixed extension at the rear of the hammer, which is engeged by the retreating bolt at another location, possibly on the other side of hammer #1. Assume in this example that hammer #1 is dead center in the receiver, with hammer #2 on it's right side, and the rear hammer #2 extension on the left side of hammer #1, when looking at the action from the back end of the rifle. The bolt has a significant amount of clearance cut or formed into it, allowing it to travel forward and backward "over" (or rather more likely, right along side) hammer #2. For safety purposes, after hammer #2 had struck the cam rod, if the weapon did not fire right away (due to delayed cartridge ignition type failure) and therefore the bolt was not traveling rearward over it, the cam rod arm would bounce back up enough under strong spring pressure (the bolt having to be under fairly strong rear spring pressure as well) to resecure the locking arm/claw around the barrel's fixed locking lugs.

There are quite a few issues that have to be worked out with the design. For example, since the trigger is doing double duty, releasing two hammers at once, getting a good, smooth, and not overly heavy trigger pull may require a lot of tinkering to get right. Since this is a semi-bullpup design, with the hammer(s) behind the pistol grip, and not immediately with the trigger in the fire group, some of the problems associated with other bullpup rifle trigger linkage issues may also affect this rifle. Since the distance between the trigger and hammer(s) is not so great in this design, when compared to the greater distances having to be overcome on other bullpup rifles, the issue shouldn't be as significant, but will still require a solid solution. This is especially so when one additionally considers that troublesome down facing ejection port in the hollow pistol grip that the trigger linkage has to work around. Getting a large 6.5 Grendel spent shell casing (as opposed to something the size of a pistol round), or a whole live 6.5 Grendel cartridge for that matter, to eject cleanly through the relatively narrow hollow pistol grip is also another issue that may require significant tinkering, but I'm sure it's doable. One of my many intents of this design is that it be ambidexterous friendly, which is why it ejects out the bottom, rather than to one side or the other. I consider this handy for other reasons as well, most of which I should think would be obvious.

Another idea I had to simplify the build process, and to improve reliability by reducing parts breakage occurances (by simply reducing the number of parts under stress that can break) is to try using a fixed solid magnetic extractor in the bolt, likely just under the bolt face. I'm not sure if that could actually work, but I'd like to try something like that out anyway. It would have other advantages as well, assuming it didn't somehow get demagnetized, which is one strike against the idea, though I don't know how that would likely happen. I'm open to just about any idea that can keep this design simple, and yet still allow it to achieve it's previously stated goals. I would appreciate any ideas or other observations you may have on this prototype concept rifle. Keep in mind, my resources to build even just one working prototype model are very limited, at least as far as tools and money available (time not being so much of an issue), so everything about the rifle has to be very simple. I won't be building my own barrel (likely to be 18" in naked length), but much of the rest of the rifle will be made from steel pipe tubing, wood, and other such scratch materials.

Billy, I'm neither engineer nor gunsmith, so I can't critique the various technical aspects of your concepts.

I will say this, however: There is nothing really new in firearms development. Anything that works has been done before, in one form or another. If your dual hammer idea was truly practical, and as affordable as you think, it would already be used in low-cost, production rifles.

I don't wish to discourage attempts at innovative thinking, but I suspect that the cost of trying to develop a low-budget, high-accuracy Grendel would end up being far higher than what you'd have to pay for an existing rifle. Plus, in all probability you would be unsuccessful in achieving the desired goal.

Damn Stanc, those are some fine words of encouragement.

That's just a really negative attitude. I like to think that people can do anything they put their mind to.

Damn Stanc, those are some fine words of encouragement.
He asked for input, not encouragement.
That's just a really negative attitude.
I gave him my honest opinion. Would you rather I lied to him, and said "Hey, that double-hammer concept is a great idea, and is sure to work. Best of all, it'll give you a rifle that cost you no more than 100 bucks!" :rolleyes:
I like to think that people can do anything they put their mind to.
A lot of people like to think that. Unfortunately, the truth is that it just ain't so.

"A man's got to know his own limitations." ~ Dirty Harry

He asked for input, not encouragement.

Fine.

I gave him my honest opinion. Would you rather I lied to him, and said "Hey, that double-hammer concept is a great idea, and is sure to work. Best of all, it'll give you a rifle that cost you no more than 100 bucks!" :rolleyes:

That's fine too.

A lot of people like to think that. Unfortunately, the truth is that it just ain't so.

"A man's got to know his own limitations." ~ Dirty Harry

I question how much innovation there would be in the world if everyone had such a negative outlook.

Limitations aren't necessarily permanent, and people often have the potential to overcome them. It's all a matter of aspiration, time, and labor.

I question how much innovation there would be in the world if everyone had such a negative outlook.
You seem to be confusing realism with negativism.
Limitations aren't necessarily permanent, and people often have the potential to overcome them.
That's true, but so is the converse. Some limitations are permanent, and people often don't have the potential to overcome them.
It's all a matter of aspiration, time, and labor.
Those three factors do indeed matter, but you left out the most important one: Ability.

Instead of criticizing my advice to the OP, why don't you give him some useful feedback on his project?

You seem to be confusing realism with negativism.

No I'm not. What are you, a bean counter? Is this all just a matter of statistics?

That's true, but so is the converse. Some limitations are permanent, and people often don't have the potential to overcome them.

Those three factors do indeed matter, but you left out the most important one: Ability.[/quote]

I'm not about to speculate on what his abilities might be.

Are you suggesting that he's retarded?

Instead of criticizing my advice to the OP, why don't you give him some useful feedback on his project?

Actually, I don't have much to say about the OP right now, thanks.

What are you, a bean counter? Is this all just a matter of statistics?
Your statement is irrational.
Are you suggesting that he's retarded?
Not at all. I'd consider that possibility in regard to someone else, though.
Actually, I don't have much to say about the OP right now, thanks.
Yeah, I figured you have no useful information for him. :rolleyes:

At least I was trying to help him avoid wasting time on a concept that seems unlikely to achieve the stated goal. If it was viable, it would've been done already. Indeed, most of the good ideas (insofar as semi- and full-auto firearms are concerned) were invented and patented by Hiram Maxim over 100 years ago. Since then, many people have tried to devise different and innovative methods of operation, but very few ever succeeded.

Not at all. I'd consider that possibility in regard to someone else, though.

And who might that be?

Yeah, I figured you have no useful information for him. :rolleyes:

It seems you "figure" a lot.

Hello again.

It's quite all right, Rambozo. I take no serious offense to stanc's reply. I was primarily asking for input, rather than encouragement, though I do like to receive occasional encouragement. Doesn't everyone? (Thanks for the support anyway, much appreciated.)

I figured it very possible, considering how relatively little is new under the sun when it comes to small arms developement, that something like this, in some form or other, has been done before. One of my reasons for posting this thread was to see if anyone knew of any other designs like this out there, and what they knew of any such designs. How were they the same? How were they different? Why, if they did not succeed, did they fail? That sort of thing. It's possible that something like this has been tried before, but it got nowhere so fast that there is little or no historical trail left behind for anyone to track down much in the way of details about it.

So far, I haven't found anything out there that very closely matches the kind of mechanism I'm envisioning. Which is too bad, because I would want to take a good look at anything like it, good or bad design that it may have been, in order to improve my chances of success, or even make me realize how hair-brained an idea this is. Either of which could save me time, which would be valuable to me in either case. Obviously, one of those results would be a bit of a disappointment, but that's just how life works out sometimes. I've certainly had my fair share of disappointment in life.

For now, I'm continuing to pursue the design idea. I'm still just in the initial stages of trying to draw up a more clearly thought out concept on paper. What I'll do from there just depends on how that turns out, and possibly on any other further input I receive from others. I still haven't had an opportunity to post this thread at the home gunsmith forum, where I would expect to get a bit more in the way of technical input. Here at this forum, I figured I'd likely just get more in the way of generalized opinion input. Which is fine. The design concept interests me enough that I want to discuss it with others, and since it's currently envisioned as a 6.5 Grendel rifle, this forum seemed like a reasonable place to start.

I look forward to reading any further valuable input. Thank you.

It's quite all right, Rambozo. I take no serious offense to stanc's reply.
If that means you took some degree of offense, you shouldn't have. No insult was intended.
I was primarily asking for input, rather than encouragement, though I do like to receive occasional encouragement. Doesn't everyone?
I'd have been pleased to give encouragement, if your project looked like it was at all doable. Unfortunately, it appears to me that you're engaging in much wishful thinking.

Retail price of $500, for an accurate, semi-auto rifle? This seems improbable, considering the cost of a quality barrel, manufacture of other components, labor cost of fitting/assembly, liability insurance, documentation, shipping, etc.

Two hammers? It's difficult enough to get a decent trigger pull with only one hammer.

Downward ejection through the pistol grip? What experience makes you think this is doable? Do you know of any selfloading rifle that has successfully done this?

A magnetic extractor? In the unlikely event it worked, apparently you're planning on restricting the rifle to shooting only steel-cased ammo? (It won't be able to use match grade, non-magnetic, brass-cased ammo.)
So far, I haven't found anything out there that very closely matches the kind of mechanism I'm envisioning. Which is too bad, because I would want to take a good look at anything like it, good or bad design that it may have been, in order to improve my chances of success, or even make me realize how hair-brained an idea this is.

For now, I'm continuing to pursue the design idea. I'm still just in the initial stages of trying to draw up a more clearly thought out concept on paper. What I'll do from there just depends on how that turns out, and possibly on any other further input I receive from others. I still haven't had an opportunity to post this thread at the home gunsmith forum, where I would expect to get a bit more in the way of technical input. Here at this forum, I figured I'd likely just get more in the way of generalized opinion input.
I doubt anybody here has the specific information you seek. Perhaps your best option is to have a patent search done. However, that might cost you as much as buying a Grendel from AA or Sabre. :eek:

No offense meant, but it looks like you want a "free lunch." TANSTAAFL. :cool:

Anyway, about the OP. The first thing that comes to my mind in regard to your objective, is the AR18 type rifles.

As far as how well something like that would do on the market, I think is really hard to say. We know how the AR18 turned up. So I think it's more a factor of marketing than anything else, and I think pricepoint certainly plays a role in that. If you market your product well below what it's market value might be, then it might actually reduce it's market value. An example of this kind of approach in the consumer market, is Highpoint. I hear that their guns aren't really as bad as what their reputation might suggest, but that's exactly the point, their reputation. I think that with a lot of things, price point can have a great impact on the percieved quality of a part. So you might not want to market something on too low of an end, else the product loses respect.

The other side of the coin is things like military contracts. Those kinds of things, I think, are great for marketability, because then there is a greater perceived quality in the part, simply because it's in use by the military. Whether the part is of higher quality or not, really doesn't matter.

Personally, I think that effort should be put into simply making something great, then marketing it for what it is, and at a competitive price point. I think there is a sweet spot in that regard.

But as for actual rifle design; I don't think it has to be entirely unique. I think Stanc is certainly right in saying that there hasn't been a whole lot of inovation. Just look at all the Bullpups, and the trouble people have been having with that. But that doesn't really matter. I don't think there needs to be a whole lot of inovation to make something better. Just look at all the various tipping barrel delayed blowback pistols there are. While technically they are very similar, it cannot really be said that they are all the same. A T-Bone is technically the same as a steakum, though practically very different.

So I think the goal should be towards simply making something better. And I think that can, and is, often done. But I think it also very important to know where it sits within the market.

But as far as your particular design ideas; the idea of the pistol grip ejection is interesting, and is used in the P90 bullpup, though I think there are limitations there in regard to what cartridges can make us of it. I think it's a good idea for something in a pistol caliber, but not so much for something like a rifle.

I also don't think it a great idea to issolate the operating system from the charge of the cartridge. I think the problem there is that you end up with an operating system that lacks the flexibility of dealing with different loads. Linking the operation to recoil or gas operation, I think is more natural in dealing with the dynamics of different loads. Take for instance the problems with the AR-15 in Vietnam; a lot of the problems were attributed to the powder used, and it's pressure curve. The problem with the dual hammer design, is that it can only possibly be tuned for one cartridge at a time, so introducing something different from that, would likely produce a lot of reliability problems, and likely to the point of catastrophic failure, being that it would be independant of what the cartridge is doing. But that's just my opinion.

Some particular things I think that would help various rifle designs, are things like carrier stroke length in relation to bolt rotation. I think that something like changing the pitch that the bolt rotates at with a greater stroke, can translate into greater leverage on the bolt, which I think can effect reliability in regard to chambering through fouled locking lugs. Though I don't know what of a problem that actually is. It would also reduce cycle rate.

Another thing ofcourse, is the operating system. I think there is something very interesting going on there with the AN-94 Abakan, with it's mixed blowback/gas operating system. It aids in cycle rate because it actually moves the whole barrel and locking assembly rearward, before the system ever unlocks. But such a system also brings to mind a pure blow back operating system with a closed rotating bolt. Why does it need a gas system in the first place? Kick the whole barrel and trunion assembly back, and let the momentum carry the carrier the rest of the way. Probably wouldn't be great for accuracy though.

Bearing surface is another thing. In this regard, I really appreciate designs like the AK and the Glock. If you notice, they cut down a lot on the rails, which reduces bearing surface, while not compromising any real additional leverage on the carrier or slide. They put the rails right where they need to be, on the very front and rear of the slide or carrier. This, I think, gives a place for debris to go, without necessarily compromising much. And in the case of the AK, it goes further buy using the gas piston as the forward guide for the carrier, which I liken to a three wheeler.

I think there is plenty of room for interesting firearm design, and I don't think that people should be discouraged from trying their hand at the things that interest them. For sure, it's no small task, but a lot of great designers already stood up to that kind of challenge before. There is little reason to believe that you can't.

Btw, I'm not trying to bump heads here, I just don't like the attitude that I perceived Stanc to be having about this. That doesn't necessarily mean that I entirely disagree with him, or any criticisms he might have towards any particular idea. I just don't like the general attitude, that's all.

Anyway, this is all just my opinion.

Anyway, about the OP.
I have to say, you gave him some fairly good feedback. Attaboy!

A couple of comments:
But as far as your particular design ideas; the idea of the pistol grip ejection is interesting, and is used in the P90 bullpup...
Not true. The P90 ejects through a hole in the stock behind the grip. It does not eject through the grip.

That is one of the problems with his concept. Every weapon that I know of that ejects downward, does so through a large opening that provides plenty of clearance for the ejected case. The necessarily small tunnel through a pistol grip poses significant (perhaps insurmountable) challenges in getting the fired case rotated more than 90 degrees after extraction, and then started on its downward path without getting stuck.
I think there is plenty of room for interesting firearm design, and I don't think that people should be discouraged from trying their hand at the things that interest them.

I'm not trying to bump heads here, I just don't like the attitude that I perceived Stanc to be having about this.
I only know that whenever I've sought feedback from others, I wanted truthful input, even if it was negative. I certainly wouldn't want potential problems to be ignored or glossed over due to a desire to be encouraging.

I think that people should be given an honest evaluation of their ideas. If that is viewed as "discouragement" by anybody, I can live with it.

I have to say, you gave him some fairly good feedback. Attaboy!

A couple of comments:

[quote]Not true. The P90 ejects through a hole in the stock behind the grip. It does not eject through the grip.

Yup, my mistake. Memory doesn't always serve me right.

I only know that whenever I've sought feedback from others, I wanted truthful input, even if it was negative. I certainly wouldn't want potential problems to be ignored or glossed over due to a desire to be encouraging.

I think that people should be given an honest evaluation of their ideas. If that is viewed as "discouragement" by anybody, I can live with it.

Maybe I took it wrong, I dunno. It's not worth elaborating on anymore.

You're quite right, the magnetic extractor idea wouldn't fly (no pun intended) with brass cased cartridges. Even if the rifle were in a different caliber, one that has relatively less expensive steel cased ammo more readily available, I wouldn't be happy with being limited to only using the steel cased ammo. Though the idea was tempting enough to consider a switch away from 6.5 Grendel, since building an inexpensive rifle that can't shoot inexpensive ammo seemed a less than optimal match. However, actually doing so would go against the overall desired goals of the rifle, and so that's no longer currently under serious consideration. In any case, I don't feel the price difference in rifle ammunition, between steel and brass cased, in the applicable calibers, is significant enough to justify such a major limitation. The cost savings on the rifle would be too little. And, as far as I know, there is no steel cased 6.5 Grendel ammo out there anyway. Though one day...who knows?

The two hammer design does not necessitate a heavy trigger pull. Likely, the way it seems it would now work is that the first hammer would trip the second hammer as the first hammer began it's forward rotation. That increases the number of parts in the rifle's fire control group, but doesn't really cause any additional smooth trigger pull issues. Reliable and consistent timing of the operating components could still be an issue, especially under adverse conditions, but that remains to be seen. More moving parts are definitely not a plus, but the rifle's overall number of moving parts is still less than a more typical gas operated design.

Isolating the operating system from the charge of the cartridge is actually more of a potential advantage than disadvantage. Gas operated systems can be quite sensitive to small variations in the dynamics of different loads, bullet weights, and a particular powder. The previous example given of powder issues early M-16 rifles had in Vietnam, is a prime supporting example of this. In the type of design we are talking about here, the only variable that matters much is muzzle velocity. Different loads will have different muzzle velocities. The difference between those various loads at the muzzle, as different from each other as they may be (which isn't that much in 6.5 Grendel compared to other cartridges), is measured in microseconds. The timed delay between the rifle firing and the second hammer unlocking the bolt has to be long enough to account for the slowest muzzle velocity load clearing the barrel, and yet quick enough to account for the fastest muzzle velocity load. While at the same time, in both situations, the bolt has to unlock fast enough that there is still sufficient energy remaining in the barrel (after the bullet has left the barrel) for the bolt to fully cycle, ejecting the spent shell casing, chambering the next round stripped off the magazine, and locking.

Now, will that be able to work? As long as we are just looking at a practical range of 6.5 Grendel loads, ones likely intended in part for use in automatic rifles anyway, and not those specialized loadings meant only for single shot rifles, then... Yeah, as long as the timing is right to cover that small velocity variable difference window, then the only real problem will be one of finding out what that timing is, and then being able to consistently get it. Of course, the rifle could have adjustable timing, just like there are gas operated rifles with adjustable gas valves, but I don't consider that to be a very good idea for this rifle. The timing would have to be set for a particular barrel length, but as this is not a rifle intended to have a quick change barrel arrangement anyway, that's not really a relevent issue.

As to cartridge cases being ejected out the bottom of the rifle through a hollow pistol grip, I don't think that is as great a problem as one might first imagine. The top of the hollow pistol grip is not immediately below the bolt, just as is the case with most other semi-automatic rifles, so there is room for the cartridge to be rotated 90 degrees downward before it even comes into contact with the top of the grip. A complex mechanism for rotating the ejected cartridge 90 degrees downward on it's way out is not necessarily required. Look at high speed still photos of cartridges being ejected from various different semi-automatic firearms, and you will often times see, at a point in their trajectory quite close to the ejection port, that the cases are already traveling at a 90 degree rotated angle away from the weapon. That ejection trajectory varies a lot between different weapon designs, but tweaking the right ejection trajectory angle from the right pre-existing design to fit the new rifle's unique requirements doesn't seem all that insurmountable a challenge to me. The 6.5 Grendel cartridge is not that big a rifle cartridge. I expect that the ejected cartridge case will bounce downward off the inside backstrap of the hollow grip, and that will be accounted for within the design. Likely, that area will be made out of rubber as a buffer. Of course, I'm not saying all that tweaking will be easy, but it is doable, and I think the benefits of that aspect of the design are desirable enough for me to put in the effort for it. I want the rifle to be short, of near bullpup legnth, but I don't want it to be a bullpup with bullpup issues, and yet I don't want the barrel too short, so I've got limited options in achieving that goal, requiring some out-of-the-box thinking.

An accurate $500 semi-automatic rifle? I suppose it depends on what you consider to be accurate. There are accurate enough for 600 yard shooting bolt action rifles out there for $500. Making accurate semi-auto rifles is typically more difficult, and therefore more expensive, due very much in part to the gas systems those rifles use. But the the rifle design I'm talking about doesn't work like those semi-autos, so those gas system accuracy issues don't apply. At least, not so much. The rifle will require a good barrel, but it doesn't have to be a custom high end barrel. Off the shelf will be good enough, and will have to do. That being said, the barrel will still likely be the most expensive part of the rifle. $500 retail per rifle is just a goal. The way the economy is these days, maybe it would end up being more like $600 per rifle, or even more in the end. I really don't know at this point. Working out a design and building a working prototype is more my concern at this point.

A "free lunch"? What "free lunch"? What are you talking about, stanc?

Trying to combine accuracy and selfloading operation with extremely low price seems to me like attempting to get something for nothing, i.e., a "free lunch."

IMO, you can have an inexpensive rifle, or you can have an accurate semi-auto. Having it all is unlikely.

Maybe I'm wrong. In any case, I wish you all the best with this project, and hope you'll keep us updated.

...attempting to get something for nothing, i.e., a "free lunch."

Heh, I would hardly call it free. lol

Let me say that prototype work is very expensive, I am in the middle of building a new rifle.
A local machine shop wanted $2000 to make 1 prototype receiver, $400 for a gas block $1100 for a bolt design.
So if you don't have your own CNC mill and lathe you better have deep pockets.
It has taken me apx 3 months to have a receiver made and 5 weeks to have a carrier made. needless to say I decided to buy a CNC lathe, it will be much cheaper in the long run.
Good luck

Thank you for the explanation, stanc. I had actually thought you meant something entirely different. I'll be sure to update here how well the project is going, as it develops. For right now, I'm busy with getting ready for the latest college semester. I'm going back to school after about a 20 year break. Maybe this time I will finally get myself a degree in something. LOL :rolleyes: Well, I certainly do hope so, as I could really use some more income these days, and something more of a career to go with it as well.

Yes, Rambozo, hardly free at all, as can be seen from builder's example.

Which by the way, builder, I think you have definitely made the right long term decision making, getting the CNC lathe. It was a tough decision, I'm sure, but think of how much more freedom you will have now with your projects, eh? If I had done something like that years ago, when I actually had the credit for it, I'm sure I'd be very glad for it now.

I'm still working out a design that looks okay on paper for now, so I'm trying not to concern myself too much with worrying about how to handle what comes after. I figure I will be better off to just take one step at a time, and not get too far ahead of myself, or I may just end up throwing my arms up in the air with the frustration of it all.

I plan to post some drawings of the basic rifle design here when I've worked up a set that I'm happy with. Thank you for all the input. It has been interesting. I appreciate it, and hope to receive more input in due time.

I agree with stan's initial point, but IMO there may be precedent for the OP's idea. Here's the first thing I thought of when I read the OP:

http://upload.wikimedia.org/wikipedia/en/thumb/2/29/M1867_1.jpg/683px-M1867_1.jpg

The OP would just be using a linear breech block instead of a rolling one, and the "second hammer" would serve the locking (or at least delay) function of the hammer in the rolling-block design.

billybc96, read up on Paul Kiraly. He favored a delayed blowback mechanism that used a light breechblock with breechface and extractor, and heavier bolt carrier. There was a lever in between them. The lower arm of the lever rested against the receiver when bolt is fully closed. Examples include the Korobov TKB-51, the French MAT LMG and the FAMAS. Not exactly what you're suggesting, but your idea also reminded me of the Kilraly system with the fulcrum of the lever moved from the breech block to the receiver...

I think an updated MAS 49/56 would make a great basis for a low-cost design. Just replace the milled receiver with a modern stamping. It doesn't get much simpler or more reliable than a rear locking tilting bolt (BREN, FN FAL, BAR, FN MAG)

http://i208.photobucket.com/albums/bb218/constructor2007/P1250028.jpg
In 5.56

Harrison, I read about your AR1 concept on your Website and I like it. After thinking it through, if I were going to try and increase reliability on an AR with a piston upper, I'd probably go the long-stroke route like an AK. So I think you're on the right track.

John

In 5.56
They say a picture is worth a thousand words, but this seems to be an exception to the rule. Please tell us about it.

It is a long stroke piston system similar to an AK, uses standard AR barrels but screwed into a trunnion not a barrel extension, it also uses AR type bolts, firing pins, and cam pins but nothing else from an AR. I have an improved bolt design made from 9310 that will work with standard extensions or the AR1 trunnion. The trunnion lugs are different from regular AR barrel extension lugs but will allow the use of a standard AR bolt if necessary.
The carrier is not like an AR, AK, HK, Fal, Masada,or SCAR.
Left side charge in front of the trunnion.
Does not need a buffer tube or buffer so folding stocks can be used.

This wasn't meant to derail the OPs post just to say it can be done, it's not easy but, it can be done.
I think it's best to start with a few minor changes to a system then go from there. Everything cost, the more you change the more it cost. It seems like every individual prototype part cost $2000 then when it goes into production you have to make 200 of each newly designed part to get the production cost down. 10 parts at $25ea(and that is very low for some parts) x 200=$50000
Then you can buy 100 barrels at $100 ea so you can see how expensive it is.
Don't get sucked in with the thought that this 1 part will only cost $10000, then there is another and another. You have to know you can finish it before you start.
Weight has to be considered, the manufacturing process, durability, reliability
and most of all KISS.

Hi guys,

I apologize for not having posted another reply any sooner then now, but this 1st semester of college has been kicking my ass. And still is, until it's over in about another 2 weeks. I'm taking classes for a CIT networking degree, and will be taking more classes this summer. Now that I've had a look at it, I'm not sure the IT thing will be for me, though that might just be pre-finals depression chomping at my heels. So, along with my other upcoming summer classes, I've also signed up for an introductory machine shop class, which is a route I may go down instead. Either way, it's a subject I need more hands on experience with and I'm looking forward to it. Hopefully that will help me along further with this and other firearm ideas I always have bouncing around in my head.

Builder, that's pretty neat, your rifle there. Is that what you've built using the equipment you just recently bought? I've not read anything more than what's right here about it. Have you tested it yet? How's it working out for you?

I've been thinking a lot recently about this Sten SMG cheap, semi-automatic rifle idea of mine, and I'm now thinking about going an even simpler route than the whole double trigger mechanism described previously, though I'm still very big on the original concept. Instead of trying to be incredibly original, I was wondering if just a better execution of prior designs might be in order, specifically a rifle that is recoil operated, with a barrel and barrel extension that recoil with a bolt locked inside for a relatively short distance, until a wedge or falling block type cam mechanism releases the bolt from the barrel/barrel extension. The bolt would then continue back much as most any semi-automatic pistol. The barrel and extension would ride above the front and rear trigger grip, possibly on something like rails (though I'm thinking maybe just along something like a rod might be better), aiding in reducing muzzle rise and felt recoil.

The magazine would still come out the side of the rifle, still likely on the left side (though that wasn't my original preference), right above the rear trigger grip, ejecting spent rounds down through that deepened hollow grip just like with the other rifle mentioned in detail before. I've actually considered having the magazine well recoil back slightly along with the barrel and extension, but with it's already being in close proximity to the shooter's face that doesn't seem like such a great idea. I just thought that last might help simplify the rifle's design even further, and who knows...it still might, with the magazine well moved forward a bit.

So this would still very much be a tube type gun, much more Sten-like in appearance than Johnson rifle-like in appearance, and hopefully just as comparably cheaper as the Sten, though the Johnson rifle actually operates more like this rifle concept than the Sten. But not really, as the Johnson was a clever but way overly complex design that was hardly cheap to manufacture, and not without it's faults. (Mainly way too many tiny, easy to lose parts, but that's just my view on the Johnson, which was an otherwise fairly successful rifle in it's very limited combat use.)

I'm curious as to what you guys think of going this above route to achieve the previously outlined goal, or sticking with something like the prior design concept instead, or possibly even going with a design mix of both? (Which would still be mostly the first rifle idea and less of this second one.)

slightly concerned about your design. admittedly i haven't checked through the whole thread but if you are using grendel rounds in a side loading config you might have a slight problem. they are lighter than full house rounds like the 7.92x57 german rounds used in the FG42 but it was complained that the centre of mass shifted as the mag emptied. also a grendel case is longer than those of 5.7x28mm pistol sized FN cases so downward ejection might have some issues.
just my 2 cents

P.S. If you don't mind that then all is good, and good luck on your project!

I haven't had much time to work on this idea recently, and may not ever at this rate...at least until I'm done with college. But then I'll be busy with a job in my field, and so...who knows, eh? Certainly with a better job I will be better able to afford resources that will make this all at least possible...if not necessarily much easier otherwise.

I have changed my thinking on the idea however, and so I wanted to update people on at least that. I've dropped my later idea of going to an essentially delayed blow-back design using some form of dropping block type mechanism, and have returned to the mechanical "two hammer" timed delay lock mechanism originally outlined in my first posting. It's simpler in it's own way, and definitely likely to be more reliable and more accurate than the later concept. The newer design does not actually use two hammers, but now currently uses, in envisioned concept at least, a striker fired design combined with just one "hammer" that doesn't do a hammer's job at all. Instead, that one hammer does the timed delay unlocking as previously described in the first post.

Other changes include my moving away from a truly tubular tube gun design. The rifle will now use square hollow steel tubing, as it is easier to work with in a lot of ways, at least for me with my limited resources, and I think the change will be better overall for the rifle as well. As an example of this, the flat surfaces of a square hollow steel tube (previously manufactured as such) make it a lot easier (read less time consuming and cheaper) to install rail mounts to the body of the rifle. The same goes for mounting the magazine well, as well as for the trigger group and hollow rear grip ejector housing.

Not much else has changed. Ejecting cartridge cases down through the hollow rear grip does not yet appear to be such an insurmountable problem. I've done several measurements in this regard, and it would seem so far that the issue is mostly a non-issue. The grip will be "deeper" than an ordinary rifle trigger grip, but not impossibly so. My only real concern there is that the grip remain comfortable even when the user has thick winter gloves on, and I'm not sure yet whether or not I can pull that off. I won't know until I get around to building a first prototype. Something I'd like to get around to sooner rather than later.

Billy,

Lots of interesting new firearms design like caseless ammo, metalstorm and so on has come out within the past 30 years. So although there are always possible problems with a new idea, persistent, intelligent, motivated people can make things happen.

When I was reading about the delayed blowback action using the 2 hammers and a rod, it made me wonder if this concept is at all similar to the toggle mechanism used on the German Luger? If so, it might not be impossible to modify it to suit your idea. But I'm really visually oriented, and may not be imagining the design your are proposing properly.

Good luck, and don't give up until YOU decide that the idea isn't worth chasing, for whatever reason (cost, logistics, manufacturing, material availability and so on).

No, it really wouldn't be anything much like a toggle locking mechanism, although the latest French assault rifle does actually use a toggle-like delayed design, combined with a fluted firing chamber. With a toggle lock, the delaying action is all pretty much in the knee joint of the toggle mechanism, which keeps everything locked together for only a very brief period of time, and which tends to be very finicky about cartridge loads. It's a nifty design in its own right, but typically requires very close machine tolerances (reducing reliability), and I don't think it's at all well suited to a rifle design emphasizing low cost manufacturing techniques/end user price.

I've had a bit of time recently to go over this design, and I've made a few changes to it. For awhile I was looking at having the magazine sticking out the left side situated behind the trigger grip, but in a slanted tube essentially screwed into the front barrel tube, meeting just in front of the magazine well. An arrangement something like what is seen on the clever little pre-WW2 French MAS 38 SMG. This would make for a lower sight radius, and possibly help absorb some recoil. However, this is still too complex an arrangement to manufacture and assemble, at least for me, especially with the tolerances required. The drawings did look nice though.

So instead, I'm back to a straight (Sten-like) round receiver tube all the way back, but retaining the magazine's position on the left side of the action, just behind the trigger grip assembly. This would eject spent shell casings to the left, instead of down through the grip as was the case in the earlier design concept. I still think ejecting down through a hollow trigger grip housing is perfectly doable, but I'm currently more interested in the rifle being close to civilian legal minimum length (26" overall length last I recall) with an 18" barrel.

Most everything else is much the same. One issue I'm having is the unlocking "hammer" running across the right side of the action, where the open ejection port is. I'd rather this mechanism be less exposed to the elements, but it can't sit on the left side where the magazine enters the receiver. I'm trying to work out how I could have its operational arch work down the inside center of the bolt carrier, in as simple a fashion as it currently does off to the right of the bolt carrier. This might be done in a somewhat unusual fashion underneath the receiver tube, where an extended streamlined "box" runs from the trigger grip to the rest of the fire group just behind the magazine housing. (This assembly is the real, transferable, lower receiver of the rifle.)

Decent weight distribution is also an issue I'm contending with at the same time, counterbalancing the current somewhat left-heavy balance that the rifle has with the side-mounted magazine. Though the magazine is now behind the trigger grip on the left, it is not far enough back to cause any problems with achieving a good cheek weld for either a right or left-handed shooter. One new issue is having to arrange (possibly through a rubber buffer outside and behind the ejection port) for ejection that does not distract someone firing the rifle left-handed.

Some small numbers of semi-automatic weapon designs out there actually eject forward (old Webley semi-auto pistols for example), via fairly simple mechanical means. So I will look into this as an option, as I don't want someone shooting left-handed to be flinching every time they fire, even though the spent case trajectory shouldn't actually be hitting them anyway.
But even a "close" trajectory is too close in my book, and probably for many others as well, so ejection has to have an elegant and practical solution that just "feels right".

Yeah, well...easier said than done, eh? LOL

Sadly, none of my basic hand drawn schematics look decent enough for me to post, but I'm still intending to get a good one posted anyway, probably a whole set of them, at some point. This will make it much easier to visualize how all this locking and unlocking is happening without using gas, or rollers, or a toggle, or whatever else. It's really pretty simple, just an issue of proper timing of the mechanism.

As a side note, even though I don't quite have the time or money (mostly money) to complete the build, I've recently purchased a complete AR lower (nice one, good price) with the intention of doing a standard 18" 6.5 Grendel gas piston build. I'm pretty excited about the project, as at least it gives me something real, worthwhile, and not too difficult to work on while I get my act together on the prototype concept.

Sounds like you are trying to come up with a modernized version of the following using a delayed blowback instead of a gas piston
http://world.guns.ru/assault/as78-e.htm
Fair warning, delayed blowback weapons are usually a bit heavier than they need to be due to the amount of mass in the bolt carrier needed to retard the mechanism, as well as imparting more inertia and wear to the lock up over time. Gas ops are much softer, and don't wear out your delay mech near as fast.

That being said, wish you all the best luck.

Edit: As a suggestion, look at designs that are chambered for 6.5 G and what Common, off the shelf parts you can use. Example: You decide to go with a recoil operated rotating bolt design, the AR bolt, carrier, barrel, and barrel extension can be modified to work in such a configuration, so you can use those parts as a "proof of concept" to start with. Use an AR or AK trigger mechanism as a starting point, since those have been beaten to death and spare parts are readdily available. Trying to invent a new trigger/hammer configuration can be an expensive proposition.
Thats basically the process that Magpul took when developing the Masada...start with what you know works, and look at how to improve it/reconfigure it into the pattern/format you want.

Oh, if you are stuck on a particular action design, like a CETME or HK style roller delayed blowback, get one and study it. As a former HK91 owner I am intimately familiar with the inner workings.

Yes, the proposed rifle would look something like a TRW LMR in layout, though the current concept would have the magazine placed a bit farther back, passed the pistol grip, and the proposed rifle is not gas operated like the TRW LMR was. Nor is the proposed design fully automatic.

It is arguable if the proposed rifle would actually be considered a delayed blowback design. The rifle does not make use of inertia in the same way as a regular delayed blowback design, but rather more like a gas operated rifle. The only difference being that the locking lugs are cammed to an unlocked position without using gas as the initiator of the unlocking process. So this rifle would fit into a somewhat different category. I suppose you could say that even a gas operated rifle is a "delayed blowback" design, with the delay coming from how long it takes gas to work its way through the system and cause the logging lugs to rotate, allowing the bolt to then be free to be forced back by...blowback forces.

I guess it all just depends on how you look at these things. I've been trying to come up with a name for this type of mechanism, but I have to admit that an easier way to describe it is simply as a delayed blowback design, even though I don't think that does it justice. For example, no great mass in the bolt/bolt carrier is needed to retard the mechanism, and there are no roller pins to wear out. All in all it is a very simple design. The only issue being proper timing for the release mechanism, and what could negatively impact it in the field, as well as building it to be wear tolerant (which could then also negatively impact precise timing). That is why I am trying to internalize the mechanism so that it is not easily getting grit stuck in it, and so it can be well and appropriately lubed. I really wish I could throw up a schematic for you of how this is intended to work, but I just don't have much time to work on the project right now.

I think when I can finally do that you will get a much clearer idea of how this rifle would operate. Optimally I'd like to do up a CAD video schematic that will show the mechanism fully cycling when fired. That would help a lot.