a few years back. I started with a .470"OD L/W barrel and went from there. At the time I made a scratch built bolt, but you could probably use a .177 bolt with a one up o ring or turn an ID taper in the barrel to fit a .22 bolt. The lathe part of the project is a piece of cake, however doing a good job of drilling and facing the TP hole using a drill press is going to be challenging for sure.
