The gun matters, but in this case it's more about the load. rvb is using a powder that burns fast, so the bullet is still in the barrel of his carbine and actually slowing down because the net force applied by friction exceeds the force exerted by the gas flow behind the bullet for the last few inches before it exits.
Guy who told me this is a mutual friend of ours and was reloading titegroup. 4 grains for Pistol. He tried backing off in the carbine to reduce the recoil in the blowback action carbine. Pretty sure it is a 16" gun but is might be a little shorter.
I follow what you are saying with the TiteGroup being a fast powder. I have a bottle of powerpistol on the shelf and have been thinking that would make for some nice full power 9mm carbine loads.