In the last few months I picked up a couple old Hopkins and Allen shotguns for cheap... Less then $100.
The first one had the breach face damaged from the firing pin breaking through. I posted photos of that a while ago. The second one was in much better condition... much better! I started to repair the damaged breach face but on acquiring the second shotgun in better condition gave it up and used the barrel from the first one to convert to .357 mag. This will be used on the good action.
Purchased two more of the Numrich .357 barrels made by Star (free shipping when you spend over $75).
I cut the old shotgun barrel down to 10" then turned the .357 barrel to match the shotgun chamber and bore. slipped the .357 barrel inside the shotgun stub barrel. It ended up as a press fit the last 1/8". Used a block of wood and hammer to drive it in. It's all held together with JB Weld epoxy.