When I first got my 35 barrel for my Contender, I tried some 15 year old factory Remingtons I had left over from a Marlin I had and I did have a couple of misfires. I attributed it to the age of the rounds. I think I had 2 out of a dozen that didn't fire and they both had primer indentions. I've since gone through another box of factory Remingtons and haven't experienced any misfires? Maybe the last box had a little diffrent shoulder on them, who knows.