A double load in a muzzle loader usually isn't a disaster. A double CHARGE might be a different story.
I remember seeing an article in the Rifleman ages ago, they wound up having to do multiple loads, (something like 7, or maybe 11) before the barrel split.
Some time ages ago, I was told,
"You aren't a true muzzleloading fanatic until...
You have loaded with no powder
You have loaded with no ball
You have double loaded
and
you have shot your ramrod, at least
twice"...
A burst barrel usually means an obstruction, like a squib bullet stuck in the bore, and then another round fired,
which gets a running start before hitting the obstruction.
The classic shotgun 12/20 burst is one example/