Minimal Barrel Wall Thickness .36 cal

[MikeEasy]

I have a lovely new (old) Hopkins & Allen underhammer .36 rifle. During it's history, some of the barrel wall around the nipple was removed (ground down?), the brass flash pan recessed into the removed area and a 1/4-28 percussion nipple installed (factory spec is 1/4-32). Around the percussion nipple the barrel wall thickness is ~3/16" (.1875"). Of course the area around the nipple is the place with the most wear, corrosion and action. I'm concerned about 3 potential problems:

a) is the barrel wall thickness of 3/16" around the nipple sufficient?

b) Might the change of nipple from 1/4-32 to 1/4-28 weaken the threads?

c) Does the ground down area (approximately heart-shaped ~5/8" dia.) around the nipple hole create a stress "shoulder" which might rupture along the edge of the removed steel?

I'm thinking of shooting it with a .36 caliber load of 30-40 grains and no more.

 

[Katahdin]

There are a few builders on the webs that still make the UH, might have to check with one and see what they can do for you.I Googled Under Hammer when I was looking for a rifle..

 

[Rifleman1776]

is the barrel wall thickness of 3/16" around the nipple sufficient?

tough one to respond to. Pics would help.
Saying "yes" would only be a guess. And guesses with stuff that goes bang is not wise. :shocked2:
My gut is telling me it would be OK. But, 'stuff' happens in the life of a gun. Some idjit, not you, might try smokeless powder or double/triple charges.
Thinking about it while I'm typing, my gut has changed it's mind.
Now, it's telling me, if it were my gun, get a new barrel. Or shorten and refit the current barrel.

 

[bob308]

as said pictures would help. your location would help. if you were close I could look at it and see what you have. could even fix it which would be easy.

 

[MikeEasy]

OK for those who want pictures:

IMGUR photo album (5 pictures) of the H & A rifle percussion nipple area that has been modified.

My feeling is that cutting out a short section of the barrel and re-breeching it is the best long-term solution.

 

[hanshi]

I've owned one, a .45, for 50 years and it came with a circular cutout where the brass flash cup was. Can't tell you much about yours but it does appear to have been hogged out deeper than what comes from the factory. If the nipple threads are different from the factory threads, that along with the possibly hogged out flash cup recess would raise a red flag. It's probably fine to shoot but "probably" isn't good enough for shooting. Re-breeching the barrel sounds like the better solution to me. Barrel thickness wouldn't worry me too much - my .36 has a 3/4" barrel - but the idea that some hack has been playing Russian roulette with it surely does.

 

[F.G. Ford]

My feeling is that cutting out a short section of the barrel and re-breeching it is the best long-term solution. [/quote]
You are absolutely right on that one.
Life is way too long missing a hand, or a part there of.
Underhammer rifles are very easy to have machined and fitted a tang/breech plug to take a chance like that.
And best of all you can keep your forearm stock, sights don't really change.
But then again, I really believe you should sell me the gun :grin:
Fred

 

[bob308]

from he pictures it looks no different then any other underhammer I have seen or own, the original flash shield is a little beat up. but it also acts as a stop for the ram rod.

as stated I have cut some barrels off and made a new patented breach.

 

[F.G. Ford]

Hello again,
In reference to your concern from tapping from 1/4-32 to 1/4-28 threads per inch, I would like to add my biased opinion.
Re-tapping from 1/4-32 to 1/4-28 leaves very little thread strength.
I would not want to be near that nipple while being fired.
You only have 5.2 threads with less than 40% contact. Scary situation!
Based on those numbers, you have barely 2.1 threads of questionable strength to endure about 18,000 psi. :shocked2:
Fred

 

[sc45-70]

I had a Hopkins&Allen underhammer 50 cal. pistol that came with a 1/4x28 nipple.

So not all H&A underhammers come with 1/4x32 thread.

SC45-70

 

[Zonie]

If your rifle is a H&A you really should examine the 1/4-28 threads in the barrel.
The first few threads may look fine but further down the hole, look for threads that look very thin or only partially there.

These H&A's typically came with the 1/4-32 thread and over the years it is possible someone rethreaded it for your 1/4-28 nipple.

Old Ford is exactly right. If the 1/4-32 thread is rethreaded to 1/4-28, the new thread will be missing its root diameter. (The finer 32 thread has a larger root (minimum) diameter).

Each new thread will be progressively thinner than it should too. For instance, the second thread will be .0045 (13%) undersize. The next thread will be .009 (26%) undersize and so forth.

Put in a simpler way, the fine tooth 32 thread per inch hole has already removed material that the courser 28 thread needs to make a full tooth.

Does this mean the gun will blow its nipple when it is fired? No, not necessarily but it does mean it is more likely to.

 

[bob308]

as stated some a 1/4-32 some are 1/4-28. I think the early guns were 1/4-32. later they were brought in line with the 1/4-28.

I have converted some of the 1/4-32 to the 1/4-28. by opening the hole to 5/16-24 making a plug drilled and taped to 1/4-28.

 

[Rifleman1776]

later they were brought in line with the 1/4-28.

I didn't know that. That change means owners of H&A rifle should exercise caution when replacing a nipple. A friend shot a nipple into his forearm using a wrong nipple. :shocked2: That is a lesson he will never forget.

 

[F.G. Ford]

BoB308 has it exactly right.
Once again IF there is enough wall thickness
Fred