In the middle of a shooting session my Stevens 325 30-30 had some kind of lock up failure.

The bolt won't stay cocked. When the bolt is pushed forward and down into the closed position it allows the striker to let down into the uncocked position.

Is this something that is easily explained? It seems as though the sear is simply not engaging. I haven't taken it apart yet since I'd like to know what is going on first.

Any advice appreciated!