I built this one

Note the postion of the pulleys and lines

Here it is just at the end of full recoil. Now look at the lines.

I shoot a 1 inch cast lead slug that weight 7 oz. Left to right 1 inch slug, two 577/450 cases, 17 HMR case.

The two guns I currently have. I also have the tube for a beer can mortar in the shop and am acquiring the material to build a bowling ball mortar.

I just acquired a round ball mould, but haven't tried it yet.