New Army "Caliber Configuration Study"

[Tony Williams]

You are making an academic comparison of the cartridges under an artificial restriction (equal barrel lengths). This methodology is used in order to show one's pet cartridge concept in the best possible light, but it seldom provides a realistic comparison of the cartridges in the barrel lengths actually used on the battlefield.

In John's hypothetical ambush scenario, he discussed 65G ARs and LMGs. The current US Army individual weapon is the M4 carbine and the LMG is the M249, both with 14.5" barrels. The USMC's M27 IAR has a 16" barrel, as does SOCOM's Mk46 LMG. Therefore, in the best case scenario, I see 16" as the maximum likely barrel length for 65G weapons.

Which means the question that really needs to be answered is how would 6.5 Grendel (7g/108gr bullet) performance from a 16" barrel compare to 7.62x54R in the 25.4" barrel PKM?

I see your point, but I completely disagree with it. The performance of cartridges needs to be compared on a like-for-like basis - i.e. using the same barrel lengths - because that demonstrates what they are capable of. Barrel lengths are not fixed in the way that cartridge dimensions are: it is a simple matter to fit a longer barrel to an MG (e.g. the British Army is planning to acquire longer barrels for its 5.56mm Para Minimis in order to improve their effective range). But once you've chosen a cartridge, you're stuck with it for a long time. The ability to use barrels of different lengths (depending on the balance between effectiveness and portability required) provides tactical flexibility for an army, but they do need to choose a cartridge which will deliver the performance they need from a barrel of acceptable length.

We have been discussing long-range performance here, in which 5.56mm weapons are frankly irrelevant - the comparison is between the Grendel and 7.62mm. And the barrel length of the M240 MG (i.e. probably 95+% of the 7.62mm MGs in US service) is - guess what? 24.5 inches! So I will concede that I maybe shouldn't have picked 20" as the comparator - it's too short, and shows the Grendel at a disadvantage.