I don't think there was a special issue of brass shotgun shells in WW 1 because we weren't over there all that long and shotguns weren't all that much in use. Lothais on the video Primer on Weapons of WW 1 brought out the difficulty of paper shells and so far as I know never mentioned brass.

I was in VN in 68-69 and can't remember seeing brass shells ever. I had a Stevens pump (I think it was) that was sawed off fore and aft as a last ditch weapon along with my M 16 but never used it and can't remember if the shells were paper or plastic but never swelled so I assume plastic.