Since the other thread got hijacked, how about a thread where we post useful “Unexpected Lessons”, learned through training, real life whatever.
A good example is USMC03’s story about the gum wrapper in the AR magazine.
Here’s a story from me to start it off–
A few years ago, I took my first tactical pistol training class, and I planned to shoot my 5" 1911, which I had been shooting in IPSC for about a year. I had a couple ammo cans of .45 reloads (mine), and I had been shooting that same recipe for about a year. What I didn’t realize is that the OAL of the rounds was “just” long enough that as many as 50% of them could get jammed when racking out live rounds-- something I never did in practice, and almost never did in IPSC (end of stage excepted). I realize this problem before the class, and reverted to my backup gun and back-up ammo (which happened to be my .40 Limited gun).
The lesson I learned is that something that has been “working forever” can still have problems when behavior and training changes-- equipment must be re-validated when training changes to check for unexpected effects.