Protocall_Design
Member
It's easy enough to back off the strain screw before removing the side plate, regardless of what state the action is in.
Judging from the picture in post #14, which I have somehow missed until now, my guess would be that the hammer was cocked too far back and rode up over the trigger. If that happens, the gun is locked up until you take it apart and untangle the hammer and trigger. If that is what actually happened, it's an easy fix. If you're looking for that, it will be obvious as soon as you get the sideplate off.
Gun in question here is a mdl60. I believe the problem could be the bolt or the lock.Same thing happened to me on a Model 60. Locked up tighter than a tick.
Upon disassembly, I discovered the bolt broken.