Lets start over: how do you design a GPC?

Lets start over: how do you design a GPC? - Printable Version

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Lets start over: how do you design a GPC? - cory - 07-09-2013

Guardsman26 Wrote:But, here comes the good news. When it comes to building a SAW variant, you can actually start with a 5.56 Minimi M249 rather than the 7.62 mm M240. So with the SAW, you can create a much lighter machine gun, but with much greater firepower.

Coming from someone who carried the SAW (no longer than I had too), starting at the SAW design is the last thing we need to do. To put it in the proper light, when breaching a room you NEVER lead with SAW gunner unless you had a death wish.

Anyways, I don't want to get this thread off topic.

We're assuming the necessary length of a tracer round is a constraint for using the Grendel. That assumption comes from another assumption that if we wanted to use a 130gr FMJ round as the primary round we need a 130gr tracer round, but what if we used approximately a 123gr Tracer round that would be shorter than the 130gr FMJ. Could the BC and charge of the Tracer round not be adjusted to match the trajectory of the 130gr FMJ or at least to the tolerance of the current 556 tracer round to the M855A1?

Lets start over: how do you design a GPC? - LRRPF52 - 07-09-2013

[Image: 65mmPracticeTracerUK.jpg]

Maybe Tony Williams could do some scaling on this pic for a Grendel-appropriate tracer. Tracers are appropriate for a beaten zone of a machine gun, so the fact that there will be shot dispersion is intentional.

One would have to identify and clarify the maximum dispersion parameters to go forward with a serious discussion about a Grendel tracer. The 123gr idea to match the form factor of a 130gr FMJ or Green projectile makes a lot of sense to me.

I also agree that the SAW/FN Minimi design is not a good starting point for a serious LMG, since its operating system is basically an inverted AK, which is why SAWs have such a problem with longevity-the action beats itself apart, and the SAW weighs as much or more than a PKM, which is insane.

You need to start with a constant-recoil receiver design, with a good feed tray cover (which the SAW actually has from the MAG58 scaled-down), and go from there with a 12lb max empty weight goal, 11lb preferred. I actually like the barrel change mechanism from the SAW more than most other machine guns. It's very fast, very simple, and very user-friendly.

Lets start over: how do you design a GPC? - JASmith - 07-09-2013

cory Wrote:...Could the BC and charge of the Tracer round not be adjusted to match the trajectory of the 130gr FMJ or at least to the tolerance of the current 556 tracer round to the M855A1?

Frankly, this looks like an idea worth pursuing. I will admit that it hadn't occurred to me.

Implementing might be a challenge, but probably doable if we don't ask for the best possible BC for the FMJ and are willing to allow a bit more manufacturing cost for the tracer to keep its BC higher. That trick, combined with carefully crafted specs for harmonizing the tracks, might lead to an interesting tracer & ball combo for the Grendel.

I am not convinced that one must go with a 130 gr 6.5 caliber projectile to have a credible replacement for the 7.62 M80 round. Take a look at the Norma 120 gr FMJ. That bullet with a BC of .428 should have comparable barrier defeat capability to the M80 at all ranges when launched at a muzzle velocity of 2600 - 2650 ft/sec. This assumes the M80 has a barrel length of 20 inches. Furthermore, we get an idea of how well that bullet can transform into a steel-core version by looking at the Barnes TSX (BC .381), the Barnes TTSX (BC .412) and the Hornady 120 gr GMX (BC .450). Any of those shapes should have enough velocity at long range to have barrier defeat potential consistent with that of the M80.

Further, the variation in BC tells us that we could indeed harmonize the FMJ and tracer even if the tracer weighs somewhat less to accommodate the trace element.

Wounding potential is another question, but I can flatly state that kinetic energy is inappropriate and misleading metric for wounding potential.

Lets start over: how do you design a GPC? - stanc - 07-09-2013

LRRPF52 Wrote:[One would have to identify and clarify the maximum dispersion parameters to go forward with a serious discussion about a Grendel tracer. The 123gr idea to match the form factor of a 130gr FMJ or Green projectile makes a lot of sense to me.

I'm curious as to how a 130gr "green" Ball round is feasible. The steel core 6.5x55 AP bullet weighs only 112gr.

The lead core 6.5x55 Tracer projectile is 120gr. Substitute copper for core material, and it'll have to be significantly longer in order to weigh 123gr.

Lets start over: how do you design a GPC? - cory - 07-10-2013

I was only using those using those weights to make my point. I do think a heavier bullet like a 130gr makes since in an LMG and possibly DMs too.

Let's say we use a 123gr ball round we can go with a 110-115gr tracer, if we go with a 115gr ball round, we go with 95-100gr tracer. I think you get my point.

I do think the LMG and rifles should have different weighted rounds developed to compliment the platform. That being said the LMG round will need to function in a rifle and vice versa.

If possible develop a round that compliments both the LMG and DMs, therefore the DMs can acquire their needed ammo by grabbing a LMG drum and delinking rounds.

Even if the LMG and rifle uses an identical round, a LMG requires link ammo in drums requiring a dedicated logistics chain. What I'm getting at is I don't believe only ONE round will benefit logistics.

Lets start over: how do you design a GPC? - cory - 07-10-2013

JASmith if we develop 2 interchangeable rounds, one for the LMG and DMs and one for carbines, I believe slightly lowering the BC of the carbine round would result in negligible losses. Just my 2 cents.

Lets start over: how do you design a GPC? - stanc - 07-10-2013

cory Wrote:I was only using those using those weights to make my point. I do think a heavier bullet like a 130gr makes since in an LMG and possibly DMs too.

I don't disagree. What I question is if it is possible to get anywhere close to 130gr in a practical lead free bullet. This has been discussed ad nauseum on the MG&A forum, and most of the knowledgeable individuals there agree that ~108gr is about max.

Quote:Let's say we use a 123gr ball round we can go with a 110-115gr tracer, if we go with a 115gr ball round, we go with 95-100gr tracer. I think you get my point.

Sure. The Swedes did that with 6.5x55 ammo. Their Tracer bullet is 20gr lighter than the Ball round. Even with that much weight difference, the Tracer still looks to be slightly longer than the Ball projectile. And, as I mentioned previously, a lead free Tracer would be longer.

Quote:I do think the LMG and rifles should have different weighted rounds developed to compliment the platform. That being said the LMG round will need to function in a rifle and vice versa.

That's technically possible, of course, but who seriously thinks the US and NATO would go for it? The Chinese tried it with 5.8x42, but have since reverted to a single loading. I think the French use 55gr for rifles, and 62gr for LMGs, but that was accidental, not planned. (Besides, do we really want to emulate the French? :eek: :p Wink

)

Lets start over: how do you design a GPC? - cory - 07-10-2013

stanc Wrote:I don't disagree. What I question is if it is possible to get anywhere close to 130gr in a practical lead free bullet. This has been discussed ad nauseum on the MG&A forum, and most of the knowledgeable individuals there agree that ~108gr is about max.

That's a good question. You've got my wheels turning Stanc. Let me throw this out there. What's the implications of a lead free bullet that's more steel and less copper, relative to the current common ratios? Could that move us towards the weight we're looking for?

stanc Wrote:That's technically possible, of course, but who seriously thinks the US and NATO would go for it?...

I'd say the odds are about as good as the US and NATO replacing the 5.56 and 7.62 with a GPC.

stanc Wrote:I think the French use 55gr for rifles, and 62gr for LMGs, but that was accidental, not planned. (Besides, do we really want to emulate the French? :eek: :p )

What can I say when the French are... No on second thought I can't say it.

Where the French blunder into a good idea. Wait one second that's not a good idea in the 5.56. There's no legitimate reason to use a smaller round in the rifle than the LMG, unless you're going to use 77 SMKs in the LMGs and DMs.

However, in the Grendel it makes a lot of sense assuming we can accomplish a round in the 130gr family.

Lets start over: how do you design a GPC? - JASmith - 07-10-2013

Cory,

Concur on going lighter with the carbine round. I will need to revisit some earlier calculations, but they indicated that we could go down to 95 -100 grains in the Grendel and get better hit probabilities out to 300-400 meters in the carbine.

Problem is that time I spend on this is time NOT spent in drafting my share of the second volume of the Grendel reloading handbook. Will need to bow out of the conversation for awhile.

Lets start over: how do you design a GPC? - stanc - 07-10-2013

cory Wrote:That's a good question. You've got my wheels turning Stanc. Let me throw this out there. What's the implications of a lead free bullet that's more steel and less copper, relative to the current common ratios? Could that move us towards the weight we're looking for?

Steel is less dense than copper, so if you make the bullet more steel, it'll move you further away from your goal of a heavy bullet.

As best I can tell, to get close to 130gr in a boat tail spitzer, it'd have to be made of solid copper. However, that type of construction wouldn't interest the US, Europe, Scandinavia, or anyone else.

Lets start over: how do you design a GPC? - SHORT-N-SASSY - 07-10-2013

woohoo Wrote:I can tell you they may notice it, look at it, and test it themselves but that doesn't mean it will go anywhere. The cartridge and platform would have to be far ahead of the current system. It must be a big company that can develop a complete system that blows everything else out of the water.
Just goofing off 5 years ago we dropped $40k into testing several different chamber and rifling designs to increase performance. It takes a lot of money to develop, test and PROVE a complete new system.
The problem I see is the military doesn't know what they want. Someone will have to prove their system and then sell the idea to the military that it IS the system they need.
Everyone at the top is going to want what THEY think they need and they will cast a shadow of doubt on every product that they as individuals don't want.
If company "A" does come up with an idea that the mil can actually agree on. The govt will snatch the design and hand it to company "C" to produce.
Sorry for the negative view but it seems that is the way our government works these days. If it was run like a business it would be a totally different game.

To those Guests looking in on this general Topic, under various titles the past couple years, and, perhaps, concluding that we're essentially where we were at the beginning of these friendly thought-provoking discussions, I would offer in addition to woohoo's Reply, above, the last four sections of Assault Rifles and Their Ammunition, By Anthony Williams http://www.quarry.nildram.co.uk/Assault.htm: "The Lessons," The Current Contenders," Lightweight Small Arms Technologies Programme (LSAT)," "Future Options." Do join us, and contribute your thoughts, as we anticipate the future of small arms technology.