20 April 2022

6.8x51mm

SIG appears to have won the contract to replace the M4 carbine and M249 SAW.

The XM5 and XM250 are chambered in 6.8x51mm aka .277 Fury.

135gr at 3,000 fps means we've abandoned intermediate power cartridges and returned to full power rounds.

The 80k psi chamber pressure is like +P+ stuff!  To the point that it requires unconventional case construction.

It's going to have a lower muzzle velocity from the 13" M5's barrel.  Edit: 2,850 fps.

Without optics, with an empty 20-round mag... 8.4 lb.  That might be with the suppressor attached... details are scanty.

The XM250 is a lot lighter than the M249.

I expect 6.8x51mm is a lot heavier than 5.56x45mm NATO, but nobody seems to be publishing the exact weight per cartridge; they're just saying it's "20% lighter than a round of equivalent power."

I'm thinking that it's about the same weight as a 7.62x51mm NATO round when they toss in all the caveats they are about the mass.

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