Where is the vise clamping on the barrel? If right over the chamber, I would think they would be about the same. Have to take a look.
My vise uses split 1 1/2" diameter bushings. Whenever I need bushings I don't have, I just make another out of 6061 round stock. Cut to length, bore, split. I use powdered resin on the bushings. Powdered sugar works as well. If any aluminum is left on the barrel, bore cleaner removes it.
I have used two different sizes of bushing halves when a barrel is not cylindrical.