In many shotshell loads utilizing the "New Fangled" Dense Smokeless Powders the powder charge is no more than 5% of the total weight being launched from the muzzle. With ordinary porting nowhere near all of these powder gases are going to be diverted. As far as recoil reduction in a shotgun goes porting is insignificant & essentially useless. I Ain't a-drilling No Holes in any of my barrels nor letting anyone else do it with my knowledge.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra