All you can do is to remeber this, and not let it ever happen again...
Mine was a true AD... a gun with a half-cock featuee (a revolver) had the lock let go, from half-cock, and fired a .22 lead-nose into a magazine for my .17 HN2... made a mess of a $25.00 magazine that was full of ammo at the time... (I didn't think the hammer could get up enough energy from half-cock, to fire a primer!)
it is only the 4 rules that saved me... gun was pointed in a safe direction, and not at someone or something irreplacable... (pointed at the top shelf of the safe...) My AD will ALWAYS remind me why we point them in a safe direction AT ALL TIMES!!!
DON'T tear yourself up over this, but also never forget...
gun and car collector.
Rare cars, and rarer guns.