Grendel and ARC Bolt what if.

[LRRPF52]

You also have to account for the thread relief cut in the barrel tennon, where the barrel extension mates to the barrel.

Bill A. went through this exercise in the beginning. If you run the MAP at 60,000psi, what is the next part that will fail?

The chamber walls will egg-out quickly, especially with stainless barrels.

So then you design a different extension and bolt set to handle the pressure, and what performance benefits do you get, aside from single point muzzle velocity figures?

Is it worth the effort down-range, and what fps gain do you have to jump to in order to achieve that?

Is it 200fps more mv, 300fps, 400fps?

The case won’t really support that with the volume, so then you’re back to looking at an AR-10, with all of its penalties.

What several companies have done now with small bolts that support .308 is to use AerMet alloys for the bolt and extension.

FN did that with the SCAR-H/SCAR-17. POF did that with the Revolution and Rogue. And now Ruger has done it with the SFAR.

The Revolution, Rogue, and SFAR are all AR-15s chambered in .308 Winchester, with lowers that have an AR-10 magazine well, FCG moved back .625”, longer firing pin tails, enlarged mag well transition port on the bottom of the upper receiver, larger bolt faces, still using AR-15 diameter barrel extensions.

You could look at an AerMet bolt and extension for 6.5 Grendel and 6mm AR if you wanted to push the pressures 10,000psi higher, for maybe 150-200fps gains.

150-200fps mv increase isn’t doing you many favors downrange, and your brass life will diminish rapidly.

Everything is a trade-off.