Our 3 lug mounts are 17-4 and our 3 lug rear cap assemblies are 17-4.  Both are nitrided, rated for 5.56mm and 300BLK supersonic, I've run them on .308.   No problems they were designed to be durable and centerfire rifle rated.  The springs in the mounts are 17-7 rated for use to 750F, so a little conservative on ROF - like 2-30 round mags full auto.

I think the external thread on the 3 lug rear cap assemble is 1.125x28TPI- that's if memory serves correct.

The accuracy would be great most likely because with our line that would mean shooting 308 through a Rev 9 or Rev 45 in the full sized config with K spacer, and that's a 9mm bore so there won't be much impact to bullet flight with something that far over bullet diameter.    We don't have any other cans that would be .308 rated for use with a 3 lug.

The Optimus is where the full auto part of that can happen on 5.56mm carbines. It is probably the most common use 3 lug centerfire rifle application.