Hopkins and Allen manufactured these underhammer rifles and pistols back in the 1960s and 1970s. I don't recall that they lasted into the 1980s.
They were said to be good rifles but never caught on. The underhammer concept is very old; some original underhammer rifles date to the 1820s, perhaps earlier.
A collector of modern black powder arms might be interested in it, if it's in nearly unfired condition. If it's got any wear or tear on it, it likely doesn't have much value as a collectible so it may be shot without guilt.
I used to see these rifles and pistols at gun shows in Spokane (Washington) in the early 1970s. Most folks preferred the Thompson Center Hawken-style rifle over them.
As I recall, the Hopkins and Allen was made in .45 caliber but not .50 caliber.
The Thompson Center was, back then, available in .50 caliber.
Then, as now, everyone wanted the bigger bore. Even if they were going to do nothing more than hang it on the wall or shoot tin cans, they wanted the "Big 50" for bragging rights.
Truth is, a .45-caliber ball will neatly kill a deer if applied within 75 yards, no more than 100 yards.
Heck, until the Pioneers reached the plains and encountered big game like elk and grizzlies, most of them carried rifles of .40 to .45 caliber, shooting a round ball.
From what I recall seeing, the Hopkins & Allen rifles were well made of good materials. If you pistol is not box-new, load it up with 20 to 30 grains of FFFG and a patched .445 ball (assuming it's .45-caliber). I remember reading many years ago that they were well-liked by black powder target pistol shooters for their accuracy.
You may have a nice shooter on your hands, provided the bore is in good shape.
Alas, too many people caught the black powder bug, grew weary of the cleaning required, then put their gun away uncleaned. Months or years later, the bore became a rusted, pitted mess.
This still goes on today.
Not long ago, in a pawn shop, I saw a nice Uberti-made 1860 Colt with badly rusted chambers and bore. Someone was too damned lazy to clean it after firing and now it's a wall-hanger, suitable only for decoration.
