I had a factory Glock 21C (.45acp compensated). It had a rectangular hole on the front top of the slide and ported barrel. I eventually sold it after I found out you couldn’t shoot snake shot out of that ported barrel.IDK if porting can be done on slide action autos, as the pressure will exert downward. And I may be completely wrong with my doubts. Canceling some muzzle rise seems the most popular application, and would DEFINITELY work on fixed barrels like revolvers, or break actions.