The Contender has a fully supported chamber, I believe, so I would say the problem was the brass it's self. Cases stretch, especially in some semi - auto's. Three or four cycles of firing, then full length resizing could cause case thinning / separation at the webb. I would purchase new brass for the Contender, and use it in that gun only. Re-size after each firing just enough for the round to chamber. You should get a lot better brass life. If you look at the brass you are using now, you may see a faint, light colored ring around the shell, just up a little on the webb. That's a sign of case separation / failure. Another way to tell is to take an empty case, and run a piece of fine wire or coat hanger down the inside of the case. If you feel a little catch or bump just above the rim, in the webb area, that means it is thinning, and will let go shortly. A picture would be helpful.
Larry
