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Black Powder Shotgun Barrel Material

Will_White

Plastic
Joined
Sep 24, 2017
I'm wanting to build a couple black powder shotguns and a punt gun/wall gun but I'm having trouble finding specs for the barrel steel, I was thinking of using seamless 4130 tubing. 1" OD a .156 or .188 wall thickness and either a 1.125 or 1.25 OD with the same wall thickness for the shotguns. Would that work? Maybe with a 8-10" sleeve to reinforce the the breach area?

Now for the the punt gun, I don't really have a frame of reference, I've seen a couple videos that look like they used 2" OD with a .25" wall but I'm not sure if they were just signal cannons or if they were functional guns.
 
DOM steel would work for black powder only, but take a look at SARCO, they had some unturned shotgun barrel blanks listed recently.
 
Do the math. Use the thick wall formula. The problem is determining what an accurate pressure value is. And don't forget a safety factor.
 
'Substantial' pressure is not much with black powder. I have quite a few pre1880's firearms and DOM has more going for it than many originals had available even.
An uncle of mine built a lot of muzzleloaders and restored a lot of originals. He remarked to me once that really almost any modern steel with a hole in it was superior to what was available and used in the 1700-1850's. he was an old school machinist and did wonderful work. Black powder is not high pressure in comparison to the smokeless powders and steel requirements for it. The fact that Damascus barrels held up with even .050" walls or less towards the muzzles was amazing to me but he still shot many of those originals with no problems ever.
 
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We did some testing here with 3/4" black pipe and 12ga 3" shotgun shells. The results show that it will withstand the pressures. Not that it makes a nice barrel, but it is probably the weakest tubing out there.
 
Do the math. Use the thick wall formula. The problem is determining what an accurate pressure value is. And don't forget a safety factor.

That's a good resource, but I'm not really sure what the numbers actually mean. For example, if I input 1.5" ID with a .5" wall thickness and a 25000 PSI pressure, which I did some research and found a couple places that say black powder cartridges pretty much max out at 25000psi with shot shells being significantly less, I get 53125. Is that the tensile strength of material needed to contain that pressure?
 
The hoop stress link is helpful, but I'm not sure exactly what the results mean. For example, if I input 1.5" ID, .5" wall, and 25000psi, which is a number I found on a couple of sites as the max pressure of black powder cartridges, I get 53125. Is that the tensile strength of material needed to contain that pressure? I've tried pudding this a couple times and it wouldn't post.
 
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53125 psi is the stress in the material given those dimensions and that pressure. My recollection is BP shotshell pressure is less than 8000 psi. I am guessing that those dimensions are for the punt gun. The real problem in sizing material for BP guns from calculations is lack of accurate pressure data. Annealed 4140 would give you some safety factor.
 
Coming back to this project, found that my source for odd lengths of steel now has seamless normalized 4130 round tube. I'm now thinking about starting small with a .375 cal musket out of .75 OD .375 ID tube. Does this seem like a good place to start?
 








 
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