You're overthinking the barrel material.
Muzzle loader pressures are not cartridge pressures. Not even close.
I would venture to say that we could make muzzleloaders out of the trashy steel pipe sold at the big box stores. We don't because there are better alternatives. Not lately though. Cuzz: Item Sold Out.
No barrel maker anywhere, except maybe Afghanistan and Pietta, is going to use steel that will blow up and kill you. Just spit balling here, but I think that would be really bad for business.
Just one man's opinion. Buy a barrel you want. Regardless of material. Your rifle will work just fine.
Be well.