New Army "Caliber Configuration Study"

[stanc]

I do agree that the Army should be presented with data on how the Grendel performs from barrels of different lengths, with the ballistics of each compared with the PKM. They could then decide what they wanted. I suspect that they would be unwilling to make a choice which would leave their troops outranged by the PKM...

The question is, would 6.5 Grendel w/108gr bullet be outranged by 7.62x54R w/148gr bullet, when 65G is fired from a 16" barrel?

I see no need to have a trajectory match. The 16" barrel L129A1 and 20" barrel Mk48 cannot have as flat of trajectory as the SVD and PKM, yet presumably are enabling UK and US troops to not be outranged?

IMO, a new Squad Common Cartridge/General Purpose Cartridge does not need to equal or exceed M80 ballistics, it just needs to provide the same engagement range capability. It seems to me that what's important is hit probability, not any specific trajectory, as indicated by use of the L129A1 and Mk48 weapons.

...choosing a short barrel for any desired ballistics would mean having to select a more powerful cartridge, resulting in more recoil and muzzle blast and a greater ammunition weight - they wouldn't want that either.

They might not want it, but that doesn't mean they wouldn't accept it. Remember, the relationship between barrel length versus recoil and muzzle blast has been known for a very long time, yet barrels keep getting shorter and shorter.

I suspect that they might end up choosing one design of belt-fed MG in two versions: light (with a light barrel of 16-18 inches and a bipod) and heavy (with a heavy barrel of 20-24 inches and normally on a tripod). Since the gun would of course be modular, they could easily attach a bipod to a heavy-barrel version if they needed to combine long range with portability. They would thereby get the benefits of a common cartridge and ammo belt and a common MG (except for the choice of barrels and mountings).

One major flaw with that idea: The CLAWS and LDAM programs indicate they want a LMG for the rifle squad, and a MMG for the platoon, with each in a different caliber. That means two different cartridges, two different belts, and no common MG.

Edit to add: the same choice would of course apply to rifles. The logical solution would be a bullpup, otherwise they would have a choice between a long barrel for the best ballistics (DMR) or a short barrel with reduced ballistics for compactness.

I agree that a bullpup rifle -- providing someone comes out with a really good design -- would be the logical choice. And I think you've hit on an excellent approach to presenting a case for a bullpup that might actually have a chance of convincing the decision makers, where previous arguments have failed.

I'm talking about your idea to show the relationship between cartridge size and power versus barrel length and weights of weapon, ammo, and magazines. My understanding is the 6.5 GPC prototype (second from left, in the photo below) delivers approximately the same muzzle velocity from a 16" barrel as 6.5 Grendel (center, below) from a 24" barrel. These two cartridges would seem to be perfectly suited to making your case.