I have an old Marlin model 99. I believe this was the predecessor to the model 60. Anyways, the problem I'm having is that 8 out of 10 rounds feed, fire and eject fine but at least once or twice every mag the bolt fails to lock all the way forward. I get a "click" and no bang, but when I pull the bolt back it leaves the round in the chamber. I have to push the bolt forward and i can feel it click when the extractors grab the rim of the case, then it will extract it just fine. The unfired round has no primer strike whatsoever on it (I'm assuming because the bolt was not forward enough for the firing pin to make contact). I have cleaned and oiled this thing to death and there doesn't seem to be any obstructions that would make the bolt hang up. Any idea what would cause this?