The Worst ND I Never Had
Let's clear something up. There is (almost) no such thing as an 'Accidental Discharge' when it comes to firearms. Oh sure, given sufficently out of spec parts and/or high primers can make the gun go BANG when it's not expected. But if you're handling a gun in good condition, with proper ammunition, it will only fire when you deactivate all safties and pull the trigger. If you hear someone say 'It just went off! I didn't touch it!', what they mean to say is: 'I was dicking around with the piece and had my booger hook on the bang switch.'
Anyway, what many people refer to as an 'Accidental Discharge', is in the vast majority of cases, a Negligent Discharge, and lots of shooters have had them. Unexpected lead flight is exactly why rules 2 and 4 are so critical. The Rules are collapsable, even if you break one, the other three will allow you to avoid catastrophe.
In my short career as a student of small arms, I have been fortunate (or observant?) enough to have never busted a cap when I didn't mean to. However, once I came close…
One fine summer, in the dawn of a short spell of unemployment, I took the opportunity to go visit unix_jedi with the pretext of investigating job opportunities. Was it my fault that my visit coincided with his club's monthly IDPA match? And that I had remembered to bring all my gear?
unix_jedi was shooting his G30, and I was shooting my then new to me USP-45F. The club ran a cold range, and after shooting a stage, we were obligated to clear the gun and holster it empty. In between stages 1 and 2, we were wandering around in the parking lot away from the firing line and jawing about guns. Of course.
I mentioned how well the USP seemed to work in trigger-cocking mode, that unlike my previous DA .45, a Beretta 8045F, I didn't have to thumb back the hammer even for a long first shot on the first stage. He asked how it compared it to his own USP-40F, and thinking on it, I drew the USP out of my holster, pointed it at the ground before us…
..and started pulling the trigger. I was about 2/3rds of the way through the DA pull when my internal safety Nazi woke up from his catnap and yelled "Hey Dummy! You're pulling the trigger on a gun you haven't cleared yet!" At that moment, the sear tripped and the hammer fell with the loudest damn CLICK I've ever heard.
Ashen mouthed and mortified, I handed the USP over to unix_jedi, who was gracious enough to wordlessly acknowledge my faux pas, and quickly cleared the gun and pulled the trigger a few times in DA mode. He pronounced it 'good', then handed it back to me. I was still slightly trembling as I cleared it again and reholstered.
If the MD had seen what I'd done, I should've been thrown out of the match. I wouldn'tve complained. Even to this day I can't think of it without a shameful shudder. But on the brighter side, I got to experience the humbling and educational effects of an ND without the usual risk of death and destruction and I'm a safer shooter for it.