Looking for opinions...So here is my question.

I bought a 32 Caliber Green Mountain
34" octagon blank.  1.115" across flats, no taper, 1137 alloy steel

The fact that it is 1137 Alloy completely escaped me when I expressed my interest and committed to purchase. Afterwards the fact that 1137 is inferior to 4140 was highlighted, I've since found some additional data on the differences between 1137 vs. 4140 CM.

Originally I had planned to have the chamber cut for the 32-40 but since the max pressure for that cartridge is about 34,000 PSI, I 'm told I can either load it with black powder only or chamber it in 32-20.

I hope some of you with experience with 1137 Alloy will advise me about its suitability with either the 32-40 or 32-20

TIA

Bob

.32-40 and .32-20 don't use the same groove diameter. If it's for one of those two it wont work for the other.
I agree that I doubt the 1137 will be any problem in either cartridge, even with smokeless charges. Not sure if you planned to hotrod it, but most guys don't get anywhere near 33,000 psi chamber pressures with their .32-40 loads.
1137 is a pretty strong steel, and actually higher grade than BP era steel barrels were.

1137 is a leaded and sulphurized steel. They add those to make it more machinable and to get a better Finnish.

Before I got into SS, I did muzzle loading and at that time (late 70's) barrel companies were using both 1137 and 12L14 for barrel steels and even with BP the muzzle loaders had blow ups, especially in cold weather.

I've seen more than one barrel blown up, and whenever it happens there's a reason like a double charge, or too hot a powder for the cartridge. Of course the owner of said barrels always wants to blame something other than their mistake when they're embarrassed. Not sure how many barrels of any kind of steel will hold up to a double charge?

I don’t know much about Green Mountain but I do know they make muzzleloading black powder barrels.  Is this possibly one of them?  What’s the twist rate?
Bob

The straight octagon (no taper) Green mountain barrels were intended for muzzle loaders and are indeed of leaded steel.

I respectfully disagree with those that feel that they are okay, because they haven't blown up yet, at fairly high pressures.   

The problem with this steel is that it fatigues, and when it does fail, it fails catastrophically.  It's difficult, if not impossible, to predict how many firings it will withstand before it fatigues, and lower pressure loads definitely reduce the possibility (extend the number of cycles before it fails).   

This is just like the same old arguments about using a Stevens 44 action or a cast Ballard action for a non-pistol centerfire.  The answer is "just don't".  There are plenty of barrels and actions out there that are perfectly suitable for the use, just use them, and use the weak actions for pistol class cartridges or rimfires, and the leaded steel barrels for true blackpowder muzzleloaders.

  There is absolutely no reason to do otherwise, except being cheap.  And, it's a hell of a lot more expensive to deal with a failure than it is to just use a suitable action/barrel.  The only thing is you know what and when the expense comes of buying a good action/barrel, you get to gamble on when and how expensive a failure will be.  Like all gambling, sometimes you come out ahead, those that shoot their rifles without failures are the winners, occasionally there's a loser and they get the bill, and the nicknames like 3 finger Will, Blind Bart, etc.

Thanks Val,

No hot rodding for me... If anything I try to find the lowest safe gallery loads. My 32-20, a CPA, was built to shoot .321 sized bullets (207 gr. MOS)
So. The 32-40 that I would like to build would ideally have a .320 groove as well.

The reason I posed the original question was based on my concern that if I did chamber this 1137 alloy barrel was to consider what some future shooters / owners of the rifle might encounter if not warned.

I guess I could stamp the Barrel 
"32-40-For Black Powder Only" sort of like the "Browning BPCR" Stamp
of years gone by. 

To the gents that posted pictures of rifles that met an untimely demise
that were built with "1137" Alloy, thanks for that vivid precautionary image.

Thanks to those that offered their experience.

RJ  

marlinguy wrote on Aug 8^th, 2025 at 4:55pm:

Were it me I would just put it in the corner and save up a few dollars and order me a 4140 CM barrel. That way no questions because you would know what you have. When building guns best err on the safe side. Bad things can happen quickly. You might even find one here from a member. Never know what folks are willing to part with...



JMH