The effect of a muzzle brake is caused by allowing some of the jet gasses to expand angled away from the bore axis. This is a true reduction in recoil. Shotgun porting has the same effect, but to a very small percentage compared to a rifle.

A gas automatic spreads the recoil force out along the time axis. The action does not come unlocked until the shot charge has left the muzzle and pressure is bled off to zero or near zero. The action is then 'floated' momentarily, spreading the recoil out in time. There is also some gas venting which has the same effect as a muzzle brake, and an unavoidable slight loss of muzzle velocity due to the energy tapped off to work the action. Nice explanation with graphs in Butler 'The American Shotgun' Winchester Press.


"The price of good shotgunnery is constant practice" - Fred Kimble