How about lessons learned or after action review? Bad drop or double charge ? I've had a powder bushing which was rated for 16 gr. Weigh 18 gr which is way over spec. On a MEC single stage shotgun reloader.
This is why I quit reloading with double based powders years ago, I missed seeing a double charge and blew up a Blackhawk .44 mag. Double based powder loads are very small to begin with so a double charge could be fairly easy to miss, those loads were generally used for low ft. per second target shooting which I never went back to and from there on just used full H-110, 296 or A.A. #9, these powders came up to the base of the loaded bullets and never showed excess pressure signs.
I have a Glock 22 and I reload my own cases. I went to the Range I went through 150 rounds. Suddenly my trigger would not allow another shot to occur. I was perplexed. I thought I had a broken trigger. The trainer in my class tried to clear the firearm to no avail. He said well you do have a broken trigger. I said well I'll take it home take the firearm apart. Well there it was a projectile was stuck in the middle of the barrel. To me this was a miracle for both me and my trainer. I'm sure you would agree. I started looking at my reload cases and noticed a very, very small bubble in the bottom of the case. I'm not sure if this caused my squib load to occur. Anyway I've ordered aRedding 40 S&W Carbide G-RX Push Thru Base Sizing Die. I hope this fixes my possible squib load.