Grendel as a Universal Infantry Cartridge

[KentuckyBuddha]

OOOOOHHHHH....that makes more sense. lol And, that is certainly a fair point!

[stanc]

We need to know two things: Case Volume and Max Operating Pressure.

As I noted, the 6.5x45 rounds I referred to are "stretched" versions of 6.5 Grendel, therefore case capacity is greater. By how much, I don't know, but enough to give a claimed MV in the realm of 100-200 fps faster, IIRC.

I haven't participated in the discussions for some time, but some attention should be paid to starting with the 25 Remington or 30 Remington case. This one can give the same volume as the 6.5 x 45 but with the same head diameter as the 6.8 SPC. It gets this with a somewhat longer case, but one that can still function within the 2.8" length of the 7.62x51.

Yes, there is one member of Tony's MG&A forum who has been developing a 6.8mm round based on the .30 Remington case. I think it's a 6.8x50, with 2.8" OAL.

The round count in a magazine of the same depth will be greater than either the 7.62x51 and the 6.5x45 and will likely be enough to make it attractive.

I doubt that. There is no difference in round count between the SPC and Grendel case diameters for magazines of the same height as a 30-rd 5.56 mag: Both have 25-rd capacity. For SPC vs 7.62, it would be 25 rds vs 23.

When you get up to 30-rd capacity for the SPC, the Grendel might be limited to 29 rds, an insignificant difference that could be compensated for by increasing mag height a mere third of an inch.

A 6.5x45 made on a "stretched" Grendel (or shortened Carcano) case not only allows a more efficient case configuration than a 6.5x50 built on a .30 Rem case, it also offers the advantage of a shorter magazine with resulting better ergonomics, and the potential for rifles and machine guns with shorter receivers (for lighter weapon weight).

[JASmith]

Stan,

Can you either post of picture of the stacking configurations for a 30 round SPC and a 29 round Grendel / Carcano?

The larger case almost certainly makes for a larger magazine, so I could see the Grendel-based magazine being fatter than the SPC magazine.

I would also like to see a definitive discussion on how a half-inch change in cartridge length has a significant impact on ergonomics.

[stanc]

Stan, Can you either post of picture of the stacking configurations for a 30 round SPC and a 29 round Grendel / Carcano?

No, but the cartridge stack heights can be calculated:

Gre 0.445 x 15 = 6.675
SPC 0.422 x 15 = 6.330

The SPC would have two 15-rd staggered columns compared to one 15-rd and one 14-rd column for the Grendel, making the total stack height of the SPC approx. the same as the Grendel's 6.675 inches.

The larger case almost certainly makes for a larger magazine, so I could see the Grendel-based magazine being fatter than the SPC magazine.

Of course. However, the difference in magazine widths would be less than 0.05" -- so small it would be virtually unnoticeable.

I would also like to see a definitive discussion on how a half-inch change in cartridge length has a significant impact on ergonomics.

Some time ago (maybe 2-3 years), one of the guys on 68forums posted a thread about an experiment he did in this regard. He taped strips of cardboard to a magazine, to build up the width and length to match cartridges of different diameters. He found that shorter, fatter mags were easier to handle than longer, thinner mags. I regret not being able to post a link, but I don't recall the thread title or author.

Whether this would be judged as having a "significant impact" on ergonomics would depend upon perception and opinion, which will no doubt vary from individual to individual. People with small hands may find the difference to be more significant than those with large hands. I know that it is much easier for me to handle an M16 mag than an M14 mag.

[JASmith]

Thanks! That helps me visualize things a bit better.

And, yes, staggering the stacks does indeed complicate assessments of magazine length, numbers of cartridges, and so on.

Another way interpreting the stack height and magazine thickness might then be that the differences in dimensions of a 30 round magazine will be effectively negligible. Further, the difference in brass weight between the stretched Grendel and the stretch Grendel may also be as close.

[stanc]

And, yes, staggering the stacks does indeed complicate assessments of magazine length, numbers of cartridges, and so on.

I did not say that. I see no such complication. For a staggered double column, double feed magazine containing an even number of rounds, total stack height will be the height of one stack plus a hair more than half the diameter of one cartridge. It's really pretty simple. Below is a drawing showing this. (Since this pic is of a single feed mag, disregard the positioning of the top four rounds.)

Another way interpreting the stack height and magazine thickness might then be that the differences in dimensions of a 30 round magazine will be effectively negligible.

Yes, I agree. Where the difference would be noticeable is with a 30-rd 7.62x51 mag vs the 30-rd GPC mags.

[woohoo]

There are easy ways to make a wildcat and rifle that will shoot them and hard ways. Murry when he first approached me was using a 7.62x45 czech that was near impossible to find and he was using 7mm bullets. I didn't have time and wasn't interested but I machined the bolts for his AR10 and new machine gun design.
Maybe a year later Prvi started selling Carcano brass again. The 7mm bullets that have good BCs are heavy, too heavy for a case with a cap of apx 42gr IMO. Using green bullets designed for optimum BC the 6.5 and 6.8 calibers work better for a 42gr cap case again my opinion. The 6.5x45 Carcano case has the same capacity and performance as the 6.5 BRX. The Carcano case will feed from a AR10 pmag...big plus. 22 Carcano cases will fit in a pmag. Magpul is making 25 round mags that may hold 27 carcano cases.
My Nexgen(AR12) uppers from 2009 are almost identical to the new DPMS GII 308 design except my design works with the old style DPMS lowers and uses any AR15 handguard. The smaller diameter barrels and bolts are a perfect fit for the Carcano case.
AS for performance, 123gr Amax 2750fps from a 20" barrel at apx 55000 psi using an optimum powder. 2800 is easy enough to reach but not at the lower pressures.
The powders are the same range that you guys are using in the Grendel...why I have been here researching.
I have a piston rifle design from 2010 that I haven't produced, it has a 2.5-2.6" OAL. Now that there are companies that will machine molds much cheaper and produce smaller runs of parts it may be feasible to build a design that uses non standard mags.
I have talked to a company rebuilding MK48s. They say it would take a new prawl and simple barrel swap to make the MK48 work with a Carcano based cartridge.

[Tony Williams]

Maybe a year later Prvi started selling Carcano brass again. The 7mm bullets that have good BCs are heavy, too heavy for a case with a cap of apx 42gr IMO. Using green bullets designed for optimum BC the 6.5 and 6.8 calibers work better for a 42gr cap case again my opinion. The 6.5x45 Carcano case has the same capacity and performance as the 6.5 BRX. The Carcano case will feed from a AR10 pmag...big plus. 22 Carcano cases will fit in a pmag. Magpul is making 25 round mags that may hold 27 carcano cases.

AS for performance, 123gr Amax 2750fps from a 20" barrel at apx 55000 psi using an optimum powder. 2800 is easy enough to reach but not at the lower pressures.
The powders are the same range that you guys are using in the Grendel...why I have been here researching.
I have a piston rifle design from 2010 that I haven't produced, it has a 2.5-2.6" OAL. Now that there are companies that will machine molds much cheaper and produce smaller runs of parts it may be feasible to build a design that uses non standard mags.
I have talked to a company rebuilding MK48s. They say it would take a new prawl and simple barrel swap to make the MK48 work with a Carcano based cartridge.

Sounds great! Go for it….

[stanc]

I have talked to a company rebuilding MK48s. They say it would take a new prawl and simple barrel swap to make the MK48 work with a Carcano based cartridge.

What would you do for links?

[stanc]

I want one of these in 6.5 Grendel:

[Trooper]

I want one of these in 6.5 Grendel:

Who makes it? It looks like a FAL on steroids.

[stanc]

Who makes it? It looks like a FAL on steroids.

It doesn't exist. It's just a drawing I found when googling "futuristic bullpup rifle."

[montana]

it doesn't exist. It's just a drawing i found when googling "futuristic bullpup rifle."

"tease"

[Trooper]

It doesn't exist. It's just a drawing I found when googling "futuristic bullpup rifle."

It still has a lot of FAL characteristics.

[nincomp]

I am always impressed when parts of a firearm can be utilized for more than one thing (example: M3 "grease gun's" wire stock/barrel cap wrench/cleaning rod).

On this new rifle, the cheek piece also doubles as a shoe horn.