I want to make a potato or golf ball gun. Would you be willing to email or PM me the details of your setup?
I have a PVC pipe, mini-marshmallow shooting, blow gun. Made it myself. It has a 19" barrel, a "thumb-hole" butt stock, fore grip, and an adjustable mouth piece. I have shot mini-marshmallows more than 20yrds. It will also shoot jellybeans, but they can't go as far, or nearly as accurate. Jellybeans also make everything sticky with the moisture in your breath. Mini-marshmallow, though, don't get nearly as sticky and fill the barrel enough that pressure is built. The stock is where the pressure is built, sending the marshmallow soaring through the air.
I will post pics when I get back from taking my wife's granny to the doc.