Been looking for something like this for a while. Website says they will sell extension bolt and upper receiver. Compatable with any AR15 handguards. Q who...
Muzzle brakes and more BEAST 2 piece (self timing brake), APA little bastard and a Muscle brake self timing (clamp type). All worked well when not running a suppressor. The BEAST is a bargain.
51 gns of RL23 under a 140 Berger Hybrid produced 3081 Fps in my 24" Criterion (QL estimated 58463PSI). I would suspect Rl 26 would do better with similar pressure.
I had a 14.5" Sabre barrel that would send Hornady factory 123's downrange @ 2480 fps. I also had an 18" custom Bartlien that sent the same ammo at the same speed.