Hubbard's was offering drop-in barrels for shotgun and rifle frames and accoutrements for the original Huntsman line several years before the new H&R added the present muzzleloading arms to their catalog. I believe it is the son of "Hubbard's Outdoor Products" originator who is running operations now... Dad's name is Ben, don't know about the son.
Ben started the company after making up stuff for himself, having been acquainted with and fond of the originals from the '70s. I had him convert a M155 Shikari to muzzleloader years ago using his spec screw-in breechplug (like the late '70s, post litigation H&R breechplug?) as I wanted a .45 cal arm.
At the time no one I spoke with (shooters, hunters, arms dealers, cottage manufacturers) had heard of the concept of such an item... closed breech, tip-up action, etc. as a muzzleloader... they looked at me like I had two heads! The only inlines available were those inconvenient open breech quasi bolt-action things, which I've never liked aesthetically, ergonomically or in regards to user-friendliness operation wise.
Then, commercial muzzleloaders were pretty much confined to sidehammer, flint or caplock early 19th century configuration. No aspersion intended on those but I thought a LATE 19th century style rifle, like the classic 'Buffalo Rifle' or British Express Rifle EXCEPT in muzzleloading, breech-priming design would be just the ticket. I even tried having one local custom gun builder alter the Shikari I had to my desired configuration, he too was at a loss to understand why. Then I heard about Ben H. and made arrangements with him.
Now more than a decade later the market is exploding with examples of this design. If Hubbard's has gotten eclipsed some as a result, it's not surprising this might happen to a small specialty vendor. Practically everyone up to blender and refrigerator makers offer some version of this 'no-brainer'... go figure!
Better late than never, I guess...
Steve