I had the same issue a week ago. I tried the rubber jar lid pad but had to resort to a Swiss army can opener. I'm glad I hadn't thrown out all of my empties.I have a couple of the little plastic boxes crosman used to sell with the belt clips on the back and the snap down lid. I wish pellets still came in those.
Whats next ... sardine cans for pellets ?
When I get a stubborn tin I put it in the freezer for a few minutes, when it comes out it opens right up without issues.