To further BBs explanation...you don't just drill holes in barrels to lose weight. The gas pushing the shot, is going forward. Action/reaction makes us feel recoil, as the gun moves backwards. When the gas is channeled through the brake, it is directed out or to the rear. Action/reaction makes the ejected gas "push" forward on the holes in brake, reducing some of the recoil. The projectile(s) has already accelerated to its potential before the brake. Losing pressure behind it, is exactly what happens when it leaves the barrel anyways. It is not a velocity leech, excepting the idea that it is ineffective barrel length, rather than solid bbl where powder could continue to burn and accelerate the projectile. It's fairly insignificant.