That ML was an inexpensive, 1970's piece of junk to start with. Low quality in all parts.
The weakest part of that gun, would normally be the drum and nipple arrangement. That it held for the second smokeless shot is amazing.

Of course, there would be those who saw this and figured they could load a little less of the H110 and get away with it. Don't do it.

A .45 or .50 side hammer ML gun will withstand a normal charge of black powder, up to about 24,000psi - nominally, which will be produced by shooting a bullet (conical) with up to 90gr. of 2F BP. Round balls, shot with black powder, rarely produce pressures over about 15,000psi in usable/normal top-end loads.

Savage made an "Inline" muzzleloader that was supposed to be able to use smokeless powder. Seems to me, the powder it was meant for was H110, (W296). This is a magnum pistol powder.
The charge was was quite small, iirc, however some people buying those things being rather stupid increased the charge or used different powder and blew them up, then attempted to sue Savage. I don't think they were successful in the suits.