Bolster type breechplug fitting can or cannot be complicated. Two different mating surfaces have to line up and mate with their counterparts at the same time and then also the octogon flats have to coincide with there counterparts on the barrel. So lets see what has to happen.
1. The end of the breech plug threads have to be tight against the end of the threads in the barrel at the shoulder where they end
2 At the same time the breechplug threads tighten up against what they are supposed to, the outside octogon shoulder has to mate up with the end of the barrel. Preferably tight enough to close up the gap to just a line.
Then after both of 1 and 2 happen the octogon flats on the breechplug and the barrel have to align. If this doesnt happen when 1 and 2 do then the flats would have to be matched up by filing or machining............
I believe you could do 1,2,and 3 with hand tools, but it would be tedious.
Bob