I could tell with my B22 that something happened during the shot cycle, it sounded very different on the shot that the spring broke, then the rifle wouldn't cock because of the bulk of the spring binding with the short piece that broke off. My 77k was different, didn't sound any different, but suddenly the rifle wouldn't cock. I think it depends on where the spring breaks, and how much breaks off. The B22 spring had 4 or 5 coils break off, and the 77k only lost 2 coils. HTH,
Mulby