Grendel LMG

[Tony Williams]

IIRC, you have a 6.5 Grendel carbine, and one in 5.56 NATO. Have you run any tests to determine if there is a significant difference in that regard?

I haven't fired a Grendel, but I have fired (back to back) HK 416 guns in 5.56mm and 6.8mm Rem (which has a very similar recoil impulse to the Grendel). I also fired a 7.62mm HK 417 in the same session. Unfortunately I wasn't allowed to fire them on full-auto but I did get a good impression of how the recoil compared (that was why I was testing them).

If you calculate the recoil energy, the 6.8mm sits half-way between the 5.56mm and 7.62mm in similar guns, but since the HK 417 is noticeably heavier than the HK 416 (thereby reducing the recoil) I would have expected the recoil of the 6.8mm to feel closer to the 7.62mm than the 5.56mm. In fact, the opposite was true - the kick of the 6.8mm felt much closer to the 5.56mm, the recoil of the 7.62mm was a much bigger step up.

This ties in with the MURG tests which compared 5.56mm with 6.8mm and concluded that there was no difference in the practical rate of aimed fire or the hit probability.

This suggests to me that there is a kind of recoil threshold below which most people can control the gun, but above which they can't. The 6.8mm Rem falls below the threshold (therefore the 6.5mm Gren should as well), the 7.62mm is clearly above it.