I did this exact same thing. I was at the range with my brand new Canik TPSF9 Elite. I loaded the first magazine with 10 rounds of 9mm but the last round loaded was in a 380 case. Unlike yours, mine went bang but the gun failed to cycle. My first impression was great, brand new gun and issues right out of the box. The 380 case was split right down the entire side of the case. I now use this method to sort all my 9mm brass after cleaning. ( ) I still find a hand full of 380 cases every couple thousand I sort. I also keep the cracked case as a reminder. The other screw up I had was the first time using an electronic scale which was set at grams instead of grains. Now that mistake never led to a problem because I did not trust the electronic scale without verifying with my beam scale. Needless to say I always use two different scales to verify my weight charge on my LNL AP.