Porting involves creating holes of various sizes and patterns in a gun barrel. The basic idea is that when you fire a paintball out of the chamber it must travel down the barrel. As it does this, it must push all the air in front of it out of the way until it exits. With the addition of holes into the barrel, the air can more easily escape the barrel. This may have some slight effect on recoil reduction, but may also make more noise as the air exits all the holes very fast. I would say it wouldn't make much of a difference in paintball guns as they aren't very accurate to begin with.