My first thought too. It is either a musket or a rifle, no such thing as a "“Musket rifle.” Another "informed" supporter of the 2nd?
There were “rifled muskets”, but that’s another different critter. I reckon it really doesn’t matter, but when someone tries to impress me, with knowledge they don’t really have, little warning bells start ringing in my head.
How many times do you think Huck really hunted, LOL?