Hammerspur, I got some information from some old timers and a old gunsmith friend of mine today. 1The Huntsman was made with a muzzleloader barrel not the 12 gauge muzzleloader barrel,2 it was sold with a kit that let you use the 209 primer and could be loaded from the breach area or the muzzle. 3The Feds were giving H&R such a hard time about the gun having to be sold as a rifle and other flack from the feds made H&R stop making the Huntsman M/L with the 209 set up and kit.
4I did however see a H&R Huntsman M/L today for sale at the gunsmiths shop, it was a .58 cal with a #11 nipple. I would of bought it, if it was a 50 Cal.
1-I think your friend is mistaken on this one... the 12ga. muzzleloader bbl. comes with ramrod and ferules, and has no chamber, ejector, etc: may have been an accessory bbl. offered for the Huntsman series as opposed to complete package... have to do some research on that.
2-
ANY inline with an easily removed breechplug can be loaded from the breech (especially true with the push-in on the old Huntsman) a la early caplock Sharps falling blocks, but you'd need to tear the paper by hand before 'closing' the action by re-inserting the breechplug.
3-That point is the same issue leading to the present H&R Co. producing a Huntsman model as well as the Sidekick... the latter's frame is too short to mount one of their centerfire cartridge/shell bbls. on, eliminating an
unregistered firearm getting out there.
The original Huntsman used the same frames as all the other rifles/shotguns produced at the time with the exception of markings and fitment of a fat firing pin intended for whacking a #11 primer... it works just fine on a 209 primer too.
4-That .58 you saw was produced in the '70's by the original H&R Co, probably has the push-in breechplug.... .50 cals are of the new, twice (?) reorganized company, and comes with a screw-in breechplug.