Building the Beer can Coehorn Mortar. I started on making a beer can size mortar. I have this piece of DOM tubing 5.25" OD. and 2.75" ID Fits a beer can nice and a tennis ball a little lose but good enough to shoot. So I cut a breach piece out on the lathe from 4" round stock with a powder chamber and made the top part concave to the shape of a ball. I'm going to shrink fit the breach piece to the barrel and weld the crap out of it and then turn it on the lathe. Im going to make it look like one of the originals in the picture of 3 different types of beds. I step ruff cut the ball part and drilled to the bottom of the chamber to make room for the boring cuter to cut the chamber. this gun will be about 75% scale and the bore will be just over 50% scale. The original 12# gun has a 4 5/8" bore.