Had a Glock trigger return spring break while the gun was sitting in a holster. So not really a full on stop the gun from working thing, but it did turn it into a single shot with out my knowing. Good thing for me I was on the way to the range to qualify with it so the range master a Glock armorar fixed it right away. Still I always carry a BU now...
Cr*p forgot about the Colt Border Patrol .357 I was issued on being sworn in. First time at the range to qualify with it fired one round and the cylinder locked up tight. Had to remove the cylinder to get it unstuck no way to pull the trigger for a second shot on the range. Glad I found that out in training!