I have about 2,000 rounds through my 15/22 and now the bolt fails to lock open on the last round. I have 3 S&W magazines and it does it on all them. I don't believe it is an ammo issue, because if I insert an empty mag and pull the charging handle back it still wont latch open. I have one mag that if you get the bolt to latch open, tipping the rifle sideways will release the bolt. Is anyone else having this problem. It's very annoying, because I don't always keep count of the rounds, so I'm dry firing the rifle more than I would like. It doesn't matter if the gun is dirty or I've just finished cleaning it. I've shot several different types of ammo and all do the same thing. HELP please!!