Build a bp cannon?

Weapontech said:
Use this website to calculate pressures and pipe sizing. It uses Barlow's formula's which are principally directed at fluid dynamics, but works fine when calculating ballistic equivalents especially with black powder.

htt p://www.engineersedge.com/calculators/pipe_bust_calc.htm

There are a number of other references on the net which will help you through bore, projectile / weight calculations to determine maximum pressures + your added safety factor. I helped a friend build a BP mountain howitzer last year using high pressure pipe and a welded and pinned breech plug. It was the perfect diameter for a tomato-paste can full of concrete.

Here is my golf-ball cannon I built many years ago using similar construction;

1851Gball.jpg


1851LHS.jpg
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That thing is so many levels of win that I have no idea where to start patting you on the back.
 
A someone said earlier the cost of running a 3.5 or a 4 inch bore would be very costly. Also the smaller bore guys in our group tend to be more accurate----------well except for Darryl and Germaine. For every increase in bore there is an exponential increase in construction.
 
there is something strange about the Barlow formula as it applies to firearms. I tried using a bore of .730 (12 guage shotgun) and wall thickness of .15 (the usual thickness of a 12 guage at the breach) and an outside diameter of 1.03". I upped the stress level to 75,000 since I think that is somewhere around the tensile strength of mild steel and the answer I got was bursting at 8700 psi, I think. I think that common shotshell pressures are in the 10 - 12,000 psi range and the shotguns obviously do not burst. There must be something that I don't understand and probably relates to the strength of the material part of the equation. I would think that stainless steel would have a much higher tensile strength than 30000 since the equation was for use in operating pressures and wall thickness for autoclaves amongst other things

cheers mooncoon
 
mooncoon said:
there is something strange about the Barlow formula as it applies to firearms. I tried using a bore of .730 (12 guage shotgun) and wall thickness of .15 (the usual thickness of a 12 guage at the breach) and an outside diameter of 1.03". I upped the stress level to 75,000 since I think that is somewhere around the tensile strength of mild steel and the answer I got was bursting at 8700 psi, I think. I think that common shotshell pressures are in the 10 - 12,000 psi range and the shotguns obviously do not burst. There must be something that I don't understand and probably relates to the strength of the material part of the equation. I would think that stainless steel would have a much higher tensile strength than 30000 since the equation was for use in operating pressures and wall thickness for autoclaves amongst other things

cheers mooncoon
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A shotgun barrel would be chromoly steel wouldn't it? I'd suspect at least 100,000 psi tensile. If not more.. I'd be curious to know the grade used.

As for stainless it depends on the grade but 416 stainless can have tensile strengths 100-200,000 psi depending on heat treatment used...
 
ShawnC6 said:
A shotgun barrel would be chromoly steel wouldn't it? I'd suspect at least 100,000 psi tensile. If not more.. I'd be curious to know the grade used.
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early 1900s vintage shotguns used a fairly soft type of steel although I have no idea what the grade description would be. I have shot factory smokeless shells in the 10 or 11,000 psi range from damascus guns without them bursting. I would not recommend doing so and my smokeless loads for skeet shooting I think are in the 7 - 8,000 psi range and I shoot them out of damascus barreled guns. Worth noting that while I do shoot smokeless in my 12 guage guns, I shoot only black powder shells in my 20 guage ones because I can't find any low pressure smokeless loads for 20 guage. Relative to guage, as the guage goes down (smaller bore), the operating pressures go up because of the smaller volume in the shell and barrel

cheers mooncoon
 
mooncoon said:
early 1900s vintage shotguns used a fairly soft type of steel although I have no idea what the grade description would be. I have shot factory smokeless shells in the 10 or 11,000 psi range from damascus guns without them bursting. I would not recommend doing so and my smokeless loads for skeet shooting I think are in the 7 - 8,000 psi range and I shoot them out of damascus barreled guns. Worth noting that while I do shoot smokeless in my 12 guage guns, I shoot only black powder shells in my 20 guage ones because I can't find any low pressure smokeless loads for 20 guage. Relative to guage, as the guage goes down (smaller bore), the operating pressures go up because of the smaller volume in the shell and barrel

cheers mooncoon
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Interesting, maybe if I see some cheap one up I'll grab it and do some tests at works.
 
I used to make replica civil war artillery and we used normalised 1045 steel... Since original guns used either bronze or cast iron for their construction, using modern steel with the same wall thickness made the guns barrels several time safer than any original... I would never use pipes, or second hand tubes of unknown metal grade that may have cracks or may be hardened and therefore brittle to make any kind of artillery... Also, if your walls are too thin, you have a pipe bomb in your hands... I have seen a "cannon" on the EE that used a threaded breech plug that used a very fine thread: that's an accident waiting to happen. Welding may results in brittle metal.... Epoxy??? WTF???

A bore sized for a soda can can also launch tennis balls and is quite ideal for a mortar... Tennis balls (not filled with concrete!) can be launched almost anywhere and will not result in roof damage or death! A pop can filled with plaster will go several hundred meters with a good charge too...
 
yes very intresting I am 70 year have my own lathe steel just built a golf ball cannon out of a 4'' sold pc of steel 26'' long works good with black powder,made wheels also lots of fun BUT safe fun,have fun boys thanks
 
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