New Army "Caliber Configuration Study"

[cory]

Will the 6.5x43 Grendel GPC work in the magazine well of the M4 platform? And how does it compare to both the 6.5x39 and 6.5x45?

I don't see how they would. The 6.5x39 barely does.

[woohoo]

Will the 6.5x43 Grendel GPC work in the magazine well of the M4 platform? And how does it compare to both the 6.5x39 and 6.5x45?

No, the OAL is 2.5" and it isn't a 6.5x43"Grendel" The Grendel is 6.5x39.
If it is based on the Carcano case like my 6.5x45 it will have 40gr capacity. The Grendel has 36gr and my 6.5x45 has 42 gr.
All of these things are being thrown out there as a GPC along with a 6.5 in a 6.8 case, none of the are...yet. Any of them could be but until the military adopts them as such they are just little known wildcats.

[Variable]

Yes - in a brass-cased cartridge a small but significant percentage of the energy developed by the propellant is used to heat up the brass case and, through that, the chamber walls. Polymer is an excellent insulator (it is reportedly possible to stick your finger in the chamber of an MG after a long burst of fire without getting burnt) so this particular element of energy loss does not occur.



That would be fascinating and a real game-changer, but I'll reserve judgment for now. Similar claims have been made in the past, the most recent a few years ago with a propellant based on rocket fuel. Apparently it sent the chamber pressures through the roof...

Having said that, my own (non-technical, and probably unrealistic) thought on gun propellant is that the form (if not chemistry) of a typical rocket motor might have advantages: that is, a solid fuel block with a central axial channel which ignites first and then burns outwards until it reaches the case walls. If feasible, this would mean that as the propellant burned outwards so the area exposed for burning would progressively increase, generating more gas and keeping the pressure curve much flatter. It would also minimise the heat transfer to the case and chamber because the burn would not reach the case walls until right at the end. The burning rate could be adjusted by the varying the shape of the axial channel (in rocket motors, the cross-section of the channel is often star-shaped to maximise the initial surface area to provide a boost phase). I suspect that a new shape of cartridge case might be needed for this to work well, though.

Very interesting idea Tony!

What if (?): A (solvent pliable) solid propellant mixture were extruded into a conventional case from the base up by a "dispensing wand" of sorts. Then after thickening a bit, a "punch" could form the center channel by being inserted through the case mouth. Kind of like forming the hollow cavity in a jacketed pistol bullet....

Dang it. You have really got me wondering now!

[stanc]

The US Army has initiated a new 'Caliber Configuration Study' to support two new programs:

CLAWS - Combat Lightweight Automatic Weapon System
Envisioned to replace carbine, rifle, DMR, and SAW. Caliber TBD from pending CCS caliber study.

LDAM - Lighweight Dismounted Automatic Machinegun
Envisioned to replace the Medium Machine Gun and possibly the HMG. Caliber TBD from the CCS caliber study.

The way I read it, CLAWS is aimed at getting a cartridge with better performance than 5.56mm, but not so large, heavy, and powerful as would be necessary to match 7.62mm capabilities.

Since LDAM would replace the 7.62mm MMG with a weapon firing a bigger, more powerful cartridge, it appears that infantry units would still have two calibers, thereby ruling out a single GPC.

Does anybody else see it that way? Does this open the possibility for US and NATO adoption of 6.5 Grendel (or a similar cartridge)?

[JASmith]

Listening to the experiences LRRPF52 relates, the CLAWS cartridge is not likely to be much larger than the 5.56mm NATO. Whether that translates to something like the 6mm or 25 cal based on the NATO cartridge (25-45 Sharps) or a (less likely) 6mm or 25 caliber variant of the 6.8 SPC like the 6.5 x 40 posted in another thread, is not real clear.

I am very sure, however, that the velocities attainable with conventional weight 6.5 caliber bullets are likely to make that caliber problematic as more and more of our real and potential adversaries adopt modern body armor.

Armies currently steeped in the culture of the 7.62x39 and the 7.62x54, however, might welcome the 6.5 Grendel. It does indeed fit the roles filled by those cartridges and would represent a substantial capability improvement without getting into the dilemma of maybe having gone too small.

[stanc]

Listening to the experiences LRRPF52 relates, the CLAWS cartridge is not likely to be much larger than the 5.56mm NATO. Whether that translates to something like the 6mm or 25 cal based on the NATO cartridge (25-45 Sharps) or a (less likely) 6mm or 25 caliber variant of the 6.8 SPC like the 6.5 x 40 posted in another thread, is not real clear.

No, it sure isn't at all clear. Whether or not a 5.56 replacement would be of minimum size and weight, as LRRPF52 wants, depends on several (sometimes conflicting) factors.

What magazine capacity is desired?

How important are weapon and ammunition weight and size?

How important is extended range capability? (The .25-45 Sharps won't do much in this regard, due to its low-BC bullet.)

How important is the ability to defeat hard body armor? (This may require a round as big and heavy as 6.8 SPC, if not bigger and heavier.)

[Tony Williams]

The way I read it, CLAWS is aimed at getting a cartridge with better performance than 5.56mm, but not so large, heavy, and powerful as would be necessary to match 7.62mm capabilities.

Since LDAM would replace the 7.62mm MMG with a weapon firing a bigger, more powerful cartridge, it appears that infantry units would still have two calibers, thereby ruling out a single GPC.

Does anybody else see it that way? Does this open the possibility for US and NATO adoption of 6.5 Grendel (or a similar cartridge)?

It is difficult to be sure exactly what this project is trying to achieve. However, the way I see it is this:

CLAWS seems to be intended to replace not just 5.56mm but also 7.62mm in light portable weapons (mainly LMGs, presumably DMRs also). Therefore a CLAWS LMG should be able to replace both versions of the Minimi: the M249 and the MK48.

LDAM seems to be intended to replace the heavy support 7.62mm MG (M240 on a tripod) plus the .50 cal HMG in the long-range anti-personnel role (tripod-mounted for sure, possibly vehicle-mounted in due course?). And may well become the sniper round, in a higher-quality loading (although that's a minor detail).

If my reading of this is correct, then I don't see the US forces accepting a CLAWS calibre which has an inferior long-range performance (at least in terms of hit probability - trajectory, flight time and wind drift) to the 7.62mm M80. Which drops you into something vaguely resembling 6.5mm Grendel (i.e. GPC) performance territory. It would be the only calibre routinely carried at squad level.

The obvious candidates for LDAM will be something like the .338 LM or .338 NM.

Of couse, even if the US Army happens to be thinking along these lines at present, what they'll end up with may be very well be entirely different....

[stanc]

LDAM seems to be intended to replace the heavy support 7.62mm MG (M240 on a tripod)...

Upon what do you base that opinion, Tony? The info from Guardsman26 says only that LDAM is "envisioned to replace the Medium Machine Gun." There's no mention of limiting LDAM to just replacing tripod-mounted 7.62mm MMGs. It sounds to me like it's intended to replace all M240 MMGs, even those carried on patrol and fired from the bipod.

[JASmith]

...If my reading of this is correct, then I don't see the US forces accepting a CLAWS calibre which has an inferior long-range performance (at least in terms of hit probability - trajectory, flight time and wind drift) to the 7.62mm M80. Which drops you into something vaguely resembling 6.5mm Grendel (i.e. GPC) performance territory. It would be the only calibre routinely carried at squad level.... ...Of couse, even if the US Army happens to be thinking along these lines at present, what they'll end up with may be very well be entirely different....

Tony, you know that I am a fan of the Grendel but I am realistic enough to recognize that we can get hit probability at least as good as the 7.62mm M80 at 1000 metres with even a 20 calibre using a case size not too different than the 5.56 NATO.

We have also seen and participated in discussions about what the bullet needs to to when it gets there. The biggest stumbling blocks for going smaller than 7.62mm appear to have been the interest in getting through common structural materials like cinder block and concrete. The trip from there through 7mm and now 6.5 mm in your discussions has been slow and sometimes painful. Nonetheless I commend you for keeping the discussions alive!

I also agree that senior civilian. military, and political figures can be a huge wild card in what actually happens.

[LRRPF52]

Everything seems to be geared towards an improvement or match to current performance for certain duty positions, while making logistics more efficient.

The two heaviest, legacy calibers in that end are:

* 7.62 NATO
* .50 BMG

If they are listening to soldiers, and also looking at over match against existing threats like the 7.62x54R PKM and modern variants, then that narrows down the performance requirements even more for a dismounted, high round count combat load that can supplant and replace 7.62 NATO.

The next question is, how small can you go in bore diameter before losing performance at distance, and still reduce weight, and hopefully recoil?

[Tony Williams]

Upon what do you base that opinion, Tony? The info from Guardsman26 says only that LDAM is "envisioned to replace the Medium Machine Gun." There's no mention of limiting LDAM to just replacing tripod-mounted 7.62mm MMGs. It sounds to me like it's intended to replace all M240 MMGs, even those carried on patrol and fired from the bipod.

LDAM is supposed to replace the use of .50 cal in the anti-personnel supporting fire role as well as the MMG, which means it needs to have a comparable hit probability at equally long ranges. While the gun can be as light as the M240 (as the GD LWMMG shows) the ammo is still going to be substantially bigger and heavier than 7.62mm, not good for portable weapons.

In any case, the M240 is too heavy to be ideal as a standard squad weapon for dismounted infantry (hence the costly efforts to develop the M240L and the adoption of the MK48), so I would expect the LDAM MMG to be concentrated in support fire elements at platoon or company level, and assigned to squads for specific missions in which its very long range will be needed.

As I said, I would expect CLAWS to be the ammo for standard infantry rifles, DMRs (probably) and bipod-mounted LMGs, with the weight of the latter being no more than the M249. The Army wants "overmatch", but it also wants weights to be reduced as much as possible.

[stanc]

...I would expect the LDAM MMG to be concentrated in support fire elements at platoon or company level, and assigned to squads for specific missions in which its very long range will be needed.

Yes, that's my view, too. Which is why I said it appears that infantry units would still have two calibers, thereby ruling out a single GPC.

As I said, I would expect CLAWS to be the ammo for standard infantry rifles, DMRs (probably) and bipod-mounted LMGs...

I agree. IMO, the question then is if CLAWS ammo needs to have the same level of performance envisioned for the notional GPC, or would a lighter weight cartridge of somewhat lesser performance be a better choice for the CLAWS/LDAM concept?

[cory]

It seems to me that if the Infantry has a 6.5mm LMG with a high BC projectile there will be no need to drag along the .338 MMG or any other MMG for that matter.

It seems like if you need more power and range than the 6.5mm offers, than your more practical course of action would be to bring along 60mm mortars.

While the 50 cal can be deployed by dismounted squads, it's in no way practical, so why should we expect a .338 MMG to be implemented in this manner. New weapons have always changed battlefield tactics. I wouldn't expect this change to be any different.

[Tony Williams]

Yes, that's my view, too. Which is why I said it appears that infantry units would still have two calibers, thereby ruling out a single GPC.

Depends on how you define GPC. At the moment the US Army has four rifle/MG cartridges used in the anti-personnel role: 5.56 x 45, 7.62 x 51, .300 Win Mag, .50 BMG. Only the first two are used in the standard rifles/MGs routinely carried by dismounted infantry; a single GPC could replace both of them in the organic squad weapons.

Not in my wildest dreams have I imagined the GPC also replacing the .300 Win Mag and the .50 BMG, even though such capabilities may occasionally be attached to squads for specific purposes.

I agree. IMO, the question then is if CLAWS ammo needs to have the same level of performance envisioned for the notional GPC, or would a lighter weight cartridge of somewhat lesser performance be a better choice for the CLAWS/LDAM concept?

Of all of the small arms western forces have faced recently, the PKM seems to have been the most problematic. The nearest western equivalent is the MK48. I can't see the US being happy to replace the MK48 with a weapon which could be outperformed by the PKM. Which implies that the GPC needs to be able to at least match the long-range hit probability of the big 7.62mm cartridges.

[Tony Williams]

It seems to me that if the Infantry has a 6.5mm LMG with a high BC projectile there will be no need to drag along the .338 MMG or any other MMG for that matter.

It seems like if you need more power and range than the 6.5mm offers, than your more practical course of action would be to bring along 60mm mortars.

While the 50 cal can be deployed by dismounted squads, it's in no way practical, so why should we expect a .338 MMG to be implemented in this manner. New weapons have always changed battlefield tactics. I wouldn't expect this change to be any different.

I don't disagree with that. Although if something like the .338 LWMMG were adopted, both the gun and its ammo would be very much easier to man-pack than the .50 BMG!