Black Powder Golf Ball Mortar (October 24th, 2009)

My little desktop cannon is pretty fun, but it just doesn't cut it anymore. I've got an uncle in Idaho who has a neighbor that made a mortar that shoots bowling balls. I thought this was quite awesome so I set out to build a scaled down version for golf balls. Not only is this cheaper, but also carries less risk of blowing myself to smithereens. I did a lot of research to find the right metal and tried and true rules of thumb so my mortar wouldn't blow up on me. There's a good forum at that's full of information on cannon building.

Finished Golf Ball Mortar

Here are the dimensions of the piece:
Barrel (DOM Seamless Tubing)
     5-1/2" long, 3/4" wall thickness, 1-3/4" inside diameter
Plug (1018 Cold Rolled Round Bar)
     1-3/4" long, 1-3/4" diameter
Trunion (1018 Cold Rolled Round Bar)
     5-1/2" long, 1-1/4" diameter

I chamfered the inside of the barrel and the outside of the plug to get a good weld. The plug was shrink fitted into the barrel and stick welded by a friend who's starting a custom offroad truck shop. Even an hour after he finished welding the barrel was too hot to pick up. Pretty impressive how thick metal retains heat.

Welding on the trunnion

The plug has a 7/8" deep, 3/4" diameter hole drilled into the center to act as a powder chamber. This means there is 1-1/4" of metal surrounding the chamber, which exceeds the "one caliber" rule of thumb. Mainly that means I can't put enough powder into the chamber to blow it up.

My vent is a 1/16" hole that runs from the outside of the barrel into the back of the powder chamber. I then drilled a 7/32" hole at the top of the vent and used a 1/4-28 tap to thread on a standard muzzleloading nipple. This means I can use #11 percussion caps to fire the mortar. Eventually I'll make some sort of lanyard activated, spring loaded hammer. But until then I've been firing the mortar with a 2lb hammer. :D

Firing the golf ball mortar

Version Two (February 28th, 2010)

I made a number of improvements to my golf ball mortar over the winter. I finally got a metal lathe so I turned down the outside a bit to make it look better. Next I made a new mortar bed out of a dead maple tree I cut down for a neighbor. It was a fairly small tree, only 6-7 inches in diameter. I debarked the trunk and let it dry for about 6 months. Then I used the joiner and planer to get 3 sides square and then ripped a few 1-1/4" boards with the table saw. Then I planed my boards down to 1" and rebuilt the sled I'd made originally. The final improvement was to use 4 sections of 5/16" threaded rod to hold it all together, and I used square nuts to give it a historical look. The mortar feels much more solid and it looks a lot better. Once it warms up some I'll stain it.

After Improvements