The breech plugs are removable, they unscrew just like any hooked breach.
It took about 40 shots out of each barrel to establish a common load(I had trouble finding a powder, wad or lack of , and bullet combination that would give me a good group because these were take off barrels) and then I regulate that load.
Most of the load work-up was at 25 yards and a small amount of regulation and the rest was done at 100 yards, once I moved back to 100 yards, I probably only put 10 shots down each side to get the regulation to were I was happy.

C