What kind of pressure are we dealing with?

[Bogie]

I'm getting ready to craft a run of black powder golfball mortars. Just wondering how thick I need to make the walls...

 

[mykeal]

Kind of depends on the material you're planning to use.

 

[Bogie]

Well, that sorta depends on the kind of pressure that we're gonna be dealing with, doesn't it?

 

[Hawg]

The breech should have a wall thickness of at least the bore diameter which in your case would be about 1.75 inch. Drawn Over Mandrel (DOM) seamless steel is the usual choice. The breech plug should be threaded in place, no welding. The plug should extend at least the bore diameter into the bore and more is better.

 

[Bogie]

So it's really that much pressure? Is it a fast spike, or what does the curve look like?

 

[Hawg]

I don't have a graph I can show you, maybe somebody else does. BP is an explosive not a propellant so it would be IMHO a sharp spike. The recommended charge for a golf ball mortar or cannon is 40 - 60 grs.

 

[Bogie]

I checked a local place. They don't carry DOM over about 0.625, but he's looking into stuff for me.

 

[Hawg]

You might go to a scrapyard and find a piece of heavy shaft like a cylinder ram and have it bored.

 

[Bogie]

Oh we can bore it... (access to full machine shop).

My machinist bud's a little busy, so I'm trying to source the pieces to make a few of these little toys...

FORE!

 

[W. C. Quantrill]

Hey Mississippi---

You used an axle out from under a box car the last time didnt you?

 

[Hawg]

Hey Mississippi---

You used an axle out from under a box car the last time didnt you?

Actually no, those are cast.

 

[W. C. Quantrill]

 

[Hawg]

W.C. Quantrill. Good one. You had me goin.

 

[W. C. Quantrill]

Chamber pressures in the Springfield .45-70 runs 24,000 to 28,000. Chamber pressure in the .45 Colt ran around 12,000 to 15,000.

70 grains under a golfball aint gonna get that wicked. I have a 1-1/2" cannon that I shoot 2 ounces in. It shoots a 2# ball. I suspect that it is getting some measureable pressure. It will poke a hole thru a car body at a quarter of a mile. Your golf ball will not create enough resistance to build that much pressure.

You would be wise to begin with some high pressure seamless tubing. It is very common in oil field and gas field operations. Then, build around it. The oil field tubing is pressure tested to 10,000 psi. It is often referred to as upset tubing. It also telescope fits as it has a 1/4" wall thickness. 1-1/2" slip fits in 2" fits in 2-1/2" which will press fit in 3". You build strength fast with it.

Golf balls are strictly regulated to be exactly 1.68" in diameter, and 1.62 ounces in weight. If you started with 1.5" upset tubing, it would be necessary to bore or hone it about ten thousandths to get the ball to go in. (0.010 of thickness off the inside all the way around creates 0.020 increase in diameter.)