Beretta PX-4 Subcompact .380ACP
This one wasn't my fault but being the experienced one, I feel responsible.
Recently took the Bro-In-Law (let's call him Dick, pun intended) who had never been shooting before to a very nice large public range. We had three of my guns, Para CCO LDA .45ACP, Beretta PX4SC 9mm, and Ruger LCP .380ACP with about 100 rounds for each. After some serious safety instructions, sight picture help, slide ops and dry fire practice, I was right behind Dick as he shot the 9, must say he did pretty well from 7 yards. Then got him on the .380 LCP, same same. As he became comfy with the process of shoot, reload 2 mags, mag in, slide release, fire, I was able to pay a little less attention to him and shoot whatever wasn't being used in the adjacent lane. I remember separating the ammo and mags, pointing them out as Small, Medium, Large and that although .380 & 9 are related, they're quite different and shall not mix.
After a few cycles of this Dick said he could handle it all himself. I kept one eye on him and soon noticed he was having FTE problems with the 9 every round and having to release, mag out, lock, release versus just release for good lockup (he wasn't riding the slide either) when loading. Since he just delved into the second box of new TBD cheapo ammo and that he knew how to safely clear problems, I chalked it up to ammo compatiblity, limp wristing, or inexperience.
Long story slightly shorter, after getting him comfy with the .45 I tried the 9 and had the same problem using mags he loaded. After seeing bronze versus copper bullets and comparing the half unboxed ammo, I realized Dick was loading the 9 mags with 380!
At first it didn't register that he'd probably been doing it all along and it fed and shot fine for the first shot. It wasn't until I connected the speed .380 ammo was vanishing with the amount of time he'd been using the 9 that the light came on. Even the range rover who tried to help him missed it and blamed it on ammo, guess he was right. When loaded with 9mm bullets, the Beretta shot fine, imagine that.
I my many years of shooting and typically having five calibers on the range at once, I've never made this mistake, shows how novices can be problems no matter how careful you are. Since .380 is '9mm short' I understand why these worked but don't recommend anyone else do this, (aside from obvious safety issues, 380 is more rare than 9). We both got a kick out of it later and my lesson learned is watch out for Dick's as you might be or related to one.:banghead:
Reminds me of a Saloon/Hotel sign, "Outlaws welcome, Inlaws call first"