I'm often amused at folks who are "deathly afraid" of shooting a Spanish or Italian built muzzle loading pistol or rifle. Having grown up around Brazilian "monkey tail" and side lock muzzle loader made with seamed tubing for a barrel, the heavy modern steel barrels of the Italian and Spanish front stuffers look over built. Anyway, I stumbled on this guy's channel and he's modern, in comparison to the 'smiths I grew up around. They did everything with hand tools and charcoal fire brazing. This guy uses power hand tools and electric welding. You can click through it to get an idea of the process of how he makes the breech plug. He's got other videos of how he makes large "cones" for use with berdan primers for shotguns. And he's got a couple videos of how he makes the inline action that goes with this inline barrel he does in the video linked below.

https://www.youtube.com/watch?v=0bBbH4gFzu4