The idea of two bullets in one case, as a possible cause, is a revelation. I'm not sure if two 225 gr. bullets could be seated in a .45 Long Colt case without being noticed, but today's presses have good leverage and it might be possible.
Anyway, it's a revelation and a warning to keep your dies clean, especially with lead bullets and any kind of sticky lubricant, such as Alox.
Or it could have been a double charge of powder.
Mystifying. I hope the shooter can remove the rest of the cartridges to identify and weigh their powder.
It's not unheard of for reloaders to finish a batch, then pour the powder in their measure back into the wrong container, such as pouring Bullseye into a 2400 container. Later, he goes to reload with 2400 and pours the 2400/Bullseye mix into his powder measure, failing to notice the contamination.
This has happened more than once.
It's why, before I pour any powder into my powder measure, I place all other powder outside of my reach. Then I pour the intended powder into a Dixie cup and look it over. It's a moment of safety that could save you or your gun.
"And lo, did I see an ugly cat. Smoke. Brimstone. Holes in parchment. And this ugly cat was much amused." --- The Prophesies of Gatodamus (1503 - 1566)