Hi. I recently acquired a H and A 58 cal underhammer. Any info on it, max loads, problems, advice, etc. would be greatly appreciated. Barrel is 1.125", 32" long and is marked Minuteman. Thanks. Dennis

I also have some Hopkins and Allen underhammers.
There is some variation in barrel diameters mine uses a 530 ball with a heavy ticking patch. It is one of the most accurate PRB guns I have owned.
The max load is 120 gr of Black or Pyrodex RS. I would not use anything else, especially if it is one of the originals.
Be sure to get nipples with the right thread as they are not 1/4 - 28 and if you force a 1/4 - 28 in it is going to weaken the threads and is liable to get blown back out.

Thanks Lee. I will be sure to use a thread gauge when I replace the nipple. I always use black powder, even in my inlines so that will not be a problem. Thanks for the help. Dennis

I have had a 58 Underhammer since 97, I re barreled my shot out 45. Started shooting it in 78 I believe I got it used then, it was a 32' barreled Offhand model, great shooter till I wore the barrel out. It had fired more than 3500 caps while in my possesion, on the .45 barrel, and it was worn out/ burned out, couldn't keep it in 4" at 50 yards.

My 58 is 29 5/8 " long, it is a Numrich barrel and I fitted it to my receiver, I cut it round in front of the for stock to save weight. that is as long as I could turn between centers in my lathe. :-)

If you have a .58 then it will take .562 or .575 balls not .530s for 54s.

I have used both 562 and 575 balls. have molds for both and 440 gr REALs. I hunt deer with 65 gr FF or RS with the RBs, sold the REAL mold as the RBs just shot better. I have hunted with 120 gr on a western hunt but realized it was a waste. even with 65 gr V, I never recovered a ball from anything harvested including an Antelope in WY in 99.

The nipple thread of a Numrich H&A ia 1/4-32, this is the same thread as a glow plug for radio controlled airplanes engines. Taps are readily available if you ever need to clean up the threads.

Since going to smokeless guns 3 years ago the Underhammer hasn't come out of the case in 3 years. Got tired of watching my rifle rust right before my eyes while hunting.