Bullet fell apart.
 

So I'm about to leave home to go to the comic shop and I check my load on my 5906. I dropped the magazine (I don't leave my gun chambered) and saw the round at the top, but the actual slug was missing and powder was spilling into my hand. I checked the chamber and the slug fell out of the mag well. Somehow or another, it came unplugged from the case : (. I'm just glad it wasn't a discharge.

What kind of ammo was it?

It's just Federal Champion 115 gr. FMJ, i:e target ammo. Got the 50 round box for 9 bucks at Wal-Mart. I've used several hundred rounds of it though and I've never had a problem with it before this. It just seems like a small fluke in their QC and I'm not too worried about it. I once bought a box of Remington UMC .38 Special and one of the rims wasn't cut right, so I couldn't fit the round in the cylinder. I'm not saying buyer beware, it's just an anecdote. I'm gonna keep the slug as it's just a ball of lead and therefore inert, but the casing still has a live primer so I don't know what to do with that.

I once had a shell casing split almost in half inside my 686. Suprisingly, the bullet was a normal .357 made by Winchester and not some reload or cheapo round

I had that happen with a 1934 dated GECO 9mm Steyr round. Fired the first 7 rounds in the clip beautifully, but on the last one, the case split as it was being fed, forcing the bullet back into it. Had to take the gun apart to get it out, there was powder everywhere. I'm just glad it split on feeding instead of firing!

I had to pull the little bastard out with my knife. Thank god it didn't ruin my 686-it's my favorite pistol