I just picked up a short barreled 20 GA 1100 for my daughter. I want to put a magazine extension on it. The extension on her Mom’s brings the magazine capacity to six and ends an inch behind the muzzle. I’m considering an extension that would bring the magazine capacity to seven rounds, but this set up would extend about two inches beyond the muzzle. This would expose the end of the magazine to hot gas, wad and pellets. Anyone have any thoughts on the idea?

You will get some scorching and powder burn but not contact with wadds or pellets.

The shot string expands at about one inch per yard with an open choke and the shot column is still inside the plastic for the first couple of yards.

Back in the 80s we had a similar setup on the department 870s using 8 round tubes. No problems except discoloration of the tube.