You 'may' not need to bore the 410, just turn the 'insert barrel' to nicely fit the chamber and rim at the back and undersize for bore most of the rest, with a snug bore riding front end dia. (or for a bigger ga., say a 20, with an O-Ring groove up toward the muzzle. Make that a snug fit inbore with some Vasoline on the O-Ring and it with slide in/out decently)
There are some barrel liners available (Track of the Wolf used to have some) that might be good for something like this. You could fit the rear of the liner into a chamber turned 'plug' to take the breech pressure.