Heat Treatment of Black Powder Barrels

[MattMaier]

I'm in the first stages of building a cap and ball revolver (direct copy of the Colt Walker). Being that the cylinder will be subject to the highest stresses being that it's the bit that holds the powder, I am not taking any chances and doing the best heat treatment that I can. That being said, I was wondering to what extent I would need to heat treat the barrel. Back in the earliest days of muzzle loaders, I know that barrels were essentially tubes of wrought iron hammered around a mandrel, but again, it doesn't tell me to what extent they were heat treated if at all.

I look forward to hearing from you.

 

[Jim Watson]

Gun barrels even now are not very hard and I doubt a black powder revolver barrel needs heat treatment at all.

And probably not the cylinder. Just what is "the best heat treatment you can?" Do you know the alloy and have a controlled temperature furnace? Trying to heat treat a cylinder in a forge or flame might do more harm than good.

 

[MattMaier]

The material in question is mild steel. I went through some basic metallurgy in my machining class and I know that mild steel can't be heat treated like high carbon steels, so the method I plan to use is case hardening. Even if it isn't necessary to heat treat metals for black powder, I want to case harden the cylinder at the very least anyway, I just feel safer doing it.

 

[rcmodel]

Case hardening adds no strength.

All it adds is a very thin hard surface to reduce wear on moving parts.

rc

 

[Old Fuff]

If case hardning had resulted in a stronger barrel and cylinder they would have done during the 19th century, but they didn't.

The Italian reproductions of cap & ball revolvers are all proof fired and stamped with proof marks to confirm they passed. They are marked "BLACK POWDER ONLY," and as long as you follow those instructions you won't get in trouble. With the stated powder you can't overcharge because the cylinder/chambers aren't long enough.

You can burst a cylinder if you leave an air space between the powder charge and ball or bullet. Whichever projectile should always slightly compress the powder charge. If you fool with heat treating the likely result is that the parts will be annealed.

 

[Jim K]

Those modern repros are a heckuva lot stronger than the original guns ever were!

Old Fuff, you wrote, "You can burst a cylinder if you leave an air space between the powder charge and ball or bullet."

I have heard and read that from many sources, but have never been able to confirm it in my tests. If it were true, I would think that every loaded cartriidge would be dangerous since very few have powder charges that fill the case. I know that none of the thousands of rounds of .38 Special target ammo, with 2.7 gr of Bullseye, never burst any barrels and there was certainly air space between the powder and the bullet.

But I heard it often about percussion revolvers, so I tried it, with varying powder charges and bullets (there is not a lot of leeway with BP, of course, but I made sure there was a gap and that the gun was held so the powder would stay to the rear.

I have heard it also about ML rifles, that if the ball/bullet is not pushed firmly down on the powder charge, the barrel will burst. I tried that too, leaving gaps from 1" to 12" with no blown barrels. Note that sometimes a ball/bullet will be loaded into a barrel that already has a ball in it and if the second ball is not seated hard on the first, the first will hit the obstructing ball and the barrel may well burst. But with one ball/bullet and a normal powder charge, I have never been able to get any burst or bulged barrel.

I wonder if you or anyone else here KNOWS of such a case, one where YOU witnessed such a case and KNOW that there was one powder charge and one bullet.

Jim

 

[Doak]

I can speak to the issue of hardening & case hardening just about anything made of steel.
Been doing it for years on pocket knives, flintlocks, revolvers, tomahawks, hand tools, dental instruments...whatever.

Fotos show a repro 1851 I picked up at a gun show circa. 1996. It had a factory mistake on it and must've found it's way into the flea market when someone discovered it.

I annealed the main frame & internals, fixed the mistake, made some replacement parts, carburized all the internals, main frame, cylinder, loading lever & ram, and left the barrel alone.

Then hardened & tempered all the carburized parts, including the cylinder: each part tempered for it's application.

Some of the colors are different looking, 'cuz they're tempering colors. Wasn't interested in case hardened beauty. I want wear resistance. Especially on the cylinder. It was so soft, from the factory, that the cylinder locking bolt would've torn it up in no time. The cylinder doesn't need to be stronger. It's prolly stronger in the elastic annealed/normalized state. Hardening to much brittles it up & makes it more likely to grenade. Case hardening keeps some of the internal elasticity while making the surface wear resistant, as already pointed out.

My process is pack carburizing w/my own almond wood charcoal, sodium carbonate, & thinned asphalt to bind them together, inside a welded up square tubing steel pot I can wire down a top on. It's very aggressive. Can diffuse a case depth of .035'' in 2.5 hrs. at 1600'F.

Barrels, on anything that goes bang, are never hardened/heat treated to my knowledge. Barrels are made from stress relieved ordnance steel. Mainly so they won't warp when machined, ie. bored, reamed, rifled, contoured...etc. Alota muzzleloading rifle barrels are made from 12L14. It's about the softest steel ya can get. Machines beautifully. Good elasticity. Very stable.

I guess hammer forged barrels must have some work-hardening effect in them.

Pulling a rifling button thru a barrel prolly work-hardens the bore surface a wee bit. Which is why bench rest shooters leave their barrels billet diameter.

Cut rifling would not.

But heat treating a finished barrel ruins it's stability. Heat treating, for improved hardness & wear resistance, puts stress into the steel. Temperature changes in stressed barrel steel makes a gun shoot around corners. :-D A cylinder is so short, that any such effects are negligible.

However, case hardening my cylinder made the cylinder pivot hole reduce in I.D. I had to make a lap to restore it's I.D., to get it back on the pin.

OK. Don't mean to sound like a knowitall. Hope you can use any of this stuff.

Let me know if I can be of help.

Doak