Excaliber wrote:That error is extremely easy to make.
I know - I didn't have any trouble at all doing exactly the same thing in my Kimber Ultra Carry several years ago.
I got exactly the same results, too - a split cartridge, no damage to the gun, and a red face.
I also made the same resolution - only one type of ammo on the bench at a time and confirmed as the right stuff for the gun in hand.
It probably happens more often that you hear. Inserting a 16 or 20 gauge shotgun shell into a 12 gauge and then following with a 12 gauge shell is probably the most common mistake.