I don't know if this qualifies but after loading thousands upon thousands of rounds of .38 spl., .357 mag., .357 maximum, and .44 mag., I picked up a 1911 (Springfield G.I. Love that gun.) and went for my first batch of reloads for it.
I bought a set of RCBS dies, a box of 100 Hornady 230 gr. XTP's, got out a pound of Unique and my Lyman manual, and set about it.
After getting past the process of rethinking the crimp concept and how it applies to a case that chambers at its mouth (felt like brain surgery at the time), I carefully assembled 50 rounds with my old Lee Hand Press. -I have a Dillon 550B but I wanted to give complete attention to every step of every round. Plus, I didn't have enough cash for another tool head, etc., that goes with a caliber change on the Dillon.-
So the batch is finished, inspected again, and boxed up for my next trip to the range. A couple days later, I go to the range. With much anticipation, I load up a mag full of my initial set of .45 ACP reloads ever, and rack the 1911's action to chamber the first round.
The slide stopped about 3/4 of the way forward and acted like it was spot-welded in that position. No way to get it to move either backwards or forward. Locked up like a bank vault with a live round down in the guts!
After fighting off the reflexive urge to spell "HELP!" in my Carhartts, I set about to disassembling the pistol and the round fell right out.
Turns out that the noses of the 230 gr. XTP's that I bought were much rounder than the regular hardball bullets. I figured that would aid in feeding since they were hollowpoints. I WAS WRONG! I then surmised that they were meant for reloading .45 COLT instead of .45 ACP. No way that bullet shape would feed in my 1911. All I could do was take 'em home, get out my bullet puller, alias "the dammit", and take them all apart. Haven't tried again since.
Thing is I don't have anything chambered for .45 LC. Maybe I oughtta put the box of bullets up for a Karma or sumpthin'.