Porting is holes in the barrel towards the front and top. This is to release gas to keep the muzzle down during recoil. I have had it done on a 338mag. rifle and it took the muzzle jump and recoil to the level of a standard 30-06 rifle. I have it on two handguns and it works good,the only thing it does that I don't like is creates more noise. Mine was done by Mag-Na-Port International. Check out their web site. Mark