I use a couple of large C clamps, with modified contact points on the screw ends to hold the barrel end down. And a hydraulic, or scissor jack, with a conduit bender head attached, to spread out the pressure, and prevent kinking. There will be a lot of spring back in a modern barrel, so you need some kind of scale to evaluate that. Most of the barrels I have done were old surplus barrels from the late nineteenth century, bought from Dixie Gun Works years ago. But, I have bent a few modern muzzleloading smoothbore barrels as well. Some of the modern ones are very springy and must be over bent a lot. The bend in some barrels will straighten out with heavy use.
Hungry Horse