BB,

Pros of Porting
Porting results in a reduction of recoil and a reduction in muzzle climb. The recoil reduction comes from the fact that some of the hot gases that would normally help propel the shotgun backward against the shooter’s shoulder (recoil) are instead directed out of the port holes.

I sometimes see porting on the side of a barrel (in terms of the gases helping to reduse muzzle rise), so I had to research that further - check it out.............FYI

http://www.learnaboutguns.com/2008/0...hotgun-barrel/

http://magnaport.com/sgun.html