Powdered up a few loads of 22 hornet that hadn't been primed. Two different times. Powder leaking from the bottom of the case.
Squib load in 38 special. My daughter in law was shooting my son's new Smith revolver when she encountered that load. Luckily the slug hung in the forcing cone and locked up the cylinder. Could have been way more than embarrassing...Really lucky!
So, now I always check the cases before powder charging and after powder charging.