I made a cannon, and have fired it

[keith44]

Two years ago I made a mini-cannon. Test firing, and just making noise on the 4th of July are the primary use of this cannon. After reading the posts of all the accidents it got me wondering if I was playing with something I failed to understand fully prior to building. I built this one to be sturdy, but the posts have me wondering. The barrel is two piece. A seamless tube with a two inch ID and 1/4 inch wall made of steel was pressed onto a piece of AMPCO that had been bored on a lathe to .565 inch ID and turned down to give a .006 inch press fit into the tube. The length of the bore is 5 inches (muzzle to end) length of barrel is 6 1/2 inches, wall thickness of Ampco is 7/16 inches. :shocked2:

I load 60 grains 2f bp, and an over powder wad, no projectile. Is this sturdy enough to be safe from barrel "bursts". I believe the operating pressure is less than 6,000 psi with this load.

Thanks

Keith

 

[guncobbler]

Keith - So your cannon has almost 1" wall thickness and no breech plug cause the inner piece was bored not all the way thru? How thick is the metal from the back side of the bore to the back end of the barrel. If it is 3/8 inch or over you should be able to sleep well at night with out worries. Smooth bores have a whole lot less barrel thickness and folks fire 1 1/2 ounces of shot in them. Love cannons. My next one has a breech plug 2' thick and wall thickness of 1 1/2 inches. GC

 

[pennsyltucky]

that would be 11/16 wall thickness.

i think it would be hard to blow that up without anything more than a paper wad loaded over the powder...

 

[keith44]

Well I tried to over build it, because I believe that nothing has ever failed due to being built too well, but the general aversion to and the failures of the average homemade water pipe cannons made me pause and just ask the "experts".

Thanks for confirming my thinking, although I would have welcomed any critisims as well.

Keith

 

[TheDoubleD]

Wall thickness over the breech should the same dimension as the diameter of the bore at the breech. Breech plug should be sweated (shrink)and then welded. Press fit is no good.

I believe you say your ID is 2 inch so the wall of your barrel over the breech should be 2 inch. That means 2 inch in all directions.

Your load is very light for that gun and there is nothing wrong with that. But ask yourself. You say the load develops 6000 psi...how many psi did it take to press that plug in?


Look throught the N-SSA Skirmish association rules and you will find guidelines for making breech plugs. http://www.n-ssa.org/NATIONAL/RULES/Rules1-2006.pdf

 

[keith44]

It has no breech plug, it is not bored through, the OD of the material it is cut from started at 2" nominal diameter, miked at something like .030 over size and was turned down to provide a .006 press fit into a nominal bore 2" of seamless tube with a 1/4 inch wall. This is mainly for mounting purposes. The Ampco (a bronze like alloy) then has a radiused shoulder that is .020" larger than the bore of the steel sleeve. Dry Ice was used to shrink the ampco, and a rose bud heated the steel tube. When pressed together in a hydraulic press, applied pressure (according to the guage) was 15,000 psi. This is over a distance of 4.5 inches to the shoulder where pressure built to 30,000 when the press stalled. The actual bore of this "mini cannon" is a mere .565" and has an overall barrel length of 6.122 inches. It was crowned with a 28 degree taper cutter. The 6,000 psi operating load is a guess based on bore size, powder charge, and if a .500 diameter patched lead ball were loaded. (See Lyman BP loading manual .54 cal section)

Keith

 

[kgrohs]

kieth good job , sounds like you have somethimng there I did the same thing a few years back, I was finally talkedout of it, but with the load your using is a real banger :grin:n and yes i believe you sould be ok with it , and as always be carefull in what your doing. kjg

 

[TheDoubleD]

It has no breech plug, it is not bored through, the OD of the material it is cut from started at 2" nominal diameter, miked at something like .030 over size and was turned down to provide a .006 press fit into a nominal bore 2" of seamless tube with a 1/4 inch wall. This is mainly for mounting purposes. The Ampco (a bronze like alloy) then has a radiused shoulder that is .020" larger than the bore of the steel sleeve. Dry Ice was used to shrink the ampco, and a rose bud heated the steel tube. When pressed together in a hydraulic press, applied pressure (according to the guage) was 15,000 psi. This is over a distance of 4.5 inches to the shoulder where pressure built to 30,000 when the press stalled. The actual bore of this "mini cannon" is a mere .565" and has an overall barrel length of 6.122 inches. It was crowned with a 28 degree taper cutter. The 6,000 psi operating load is a guess based on bore size, powder charge, and if a .500 diameter patched lead ball were loaded. (See Lyman BP loading manual .54 cal section)

Keith

I think I missed something here.


You have a piece of bronze bored .565 and turned on the outside 2.00 inch. Correct?

And you have a piece of steel seamless tubing that has a bore of 2.00 and walls 1/4 inch thick giving an outside diameter of 2.5 inches. Is this correct?

The bronze tube was then pressed into the seamless tube. Is that correct?

Why?

 

Ampco is an extremely hard bronze alloy, tough enough to cut some steels even. But, I do not know what type of Ampco you have actually used, as there's around 9 different types. The seamless tube should be safe enough. But what frets me is the bronze inner core. Should this be an aluminium or silcon alloy, it may fracture in time and what was to be a blank firing turn into a dangerous blast of grapeshot. Yes, as many can atest I can be a nervous nelly. But I didn't get my cannoneer certification by being careless.

Also, usually the bronze is on the outside with a steel insert. And even that can be dangerous if the wrong materials are used. A brittle bronze or iron, around even a safe seamless tube, may fracture and send dangerous sharpnel flying in all directions upon firing. Especially, if it is a tight pressed fit. The exterior metal will already have a stress load and the swelling of the inner tube with heat and the pressure of firing a charge may cause the outer shell's structural integrity to fail.

CP

Two years ago I made a mini-cannon. Test firing, and just making noise on the 4th of July are the primary use of this cannon. After reading the posts of all the accidents it got me wondering if I was playing with something I failed to understand fully prior to building. I built this one to be sturdy, but the posts have me wondering. The barrel is two piece. A seamless tube with a two inch ID and 1/4 inch wall made of steel was pressed onto a piece of AMPCO that had been bored on a lathe to .565 inch ID and turned down to give a .006 inch press fit into the tube. The length of the bore is 5 inches (muzzle to end) length of barrel is 6 1/2 inches, wall thickness of Ampco is 7/16 inches. :shocked2:

I load 60 grains 2f bp, and an over powder wad, no projectile. Is this sturdy enough to be safe from barrel "bursts". I believe the operating pressure is less than 6,000 psi with this load.

Thanks

Keith

 

[keith44]

As stated already, the steel is mainly for mounting purposes, but in the event that the bore should bulge, I hope the seamless tube to contain the bronze, and disallow rapid dis-assembly. Not totally prevent failure, but rather keep things contained long enough to detect a problem.

Keith

 

[keith44]

The ampco alloy used was recommended by a tool maker friend of mine, I'll post the exact alloy when I can verify my memory. I do recall the tensile strength to be 52,000 psi.

Keith

 

[keith44]

Hmmm, correction, 30,000 psi tensile strength. It is alloy 660: copper, tin,lead, zinc, and iron blend. At any rate, it is a malliable alloy, and maintains shape and size to 14,000 psi.