I would intrepret the description "old HF minie rifle" as meaning a US 1841 (Mississippi) bored out to .58 at
Harpers Ferry--many were during the mid to late 1850s--after US Ordnance adopted .58 as std size. The
US 1855 two band rifles were also called "HF rifles," but I don't think they would have been referred to as
"old" during the US Civil War. The US 1855 was considered modern, and the evolution of the US models
continued with the US 1861, which was considered "state of the art."
Some US 1842 muskets were rifled at HF, but these were not referred to as "minie rifles." They were large
caliber (.69) behemoths with a 42" barrel. The 42s were mostly called "muskets" or "rifled muskets." Usually
minie refers to the .58 US Ord Dept round, the minie ball. Who knows? If I were a betting man, I'd say they
were US 1841s...a weapon that was far from obsolete during the US Civil War, twenty years after it was first
introduced.