This is what I use to unbreech my barrels. It is a 6" (wide) Wilton vice from Lowes. 2 strips of an old brass kickplate off a door. The least amount of material you have between the barrel & the jaw, the better. Adding wood & more padding just gives & is more prone to let the barrel rotate in the vice. This works extremely well & I have unbreeched probably 75 barrels with it with no issues.
One think I will suggest...... If this is a Precarve & it came with the barrel inlet cut, and the inlet not cut flat at the breech end where you can just drop the barrel in....... You best inlet the Lock Inlet FIRST, so you know how far to set the breech end of the barrel back to accommodate for the vent or vent liner. If you don't you could end up with the vent hole right in the middle of the breech plug.
I have built over 40 precarves...... every single one of them had to have the barrel moved back to get the vent liner where I wanted it, including 2 Chambers kits. Now some guys like the vent hole barely clearing the breechplug face. I want the vent Liner fully in from of the breechplug face & the vent liner & breechplug thread
not to intersect.
So some consideration must be made on this Before ya put the barrel in. Thus I suggest ya do the Lock in 75% of the way, then put the barrel in & find the correct location to suit you.
Building from a blank, you would do the barrel first, then the lock.
Keith Lisle
PS: If it is a Rice barrel. if will be breeched correctly. I have 100% confidence in them. I have unbreeched over 100 of their barrels & every single one was breeched perfectly & the witness marks were still there to show it.
That being said, I still unbreech every single barrel I get in, regardless of who made it. 50% of the Colerain barrels I get have to be rebreeched because of the gaps at the breechface.