Hey Roy, when you drilled the recess, did you start out with the correct size drill (minor diameter), or did you use smaller drills and progressively work up to the final size? Bill
I drilled and tapped for breeches in mid 70's following Jim Carmicheal(sp) how to in a book he wrote. I used the drill press with table turned vertical and vise mounted solid . Didnt have a problem , just worked slow .
Big difference between a lathe and a make shift drill press or a light duty drill press either. Remember the poster is talking about a 5/8 dia give or take end mill. Regardless there is no dire need for a square internal shoulder. The 82 degree shoulder coupled with a matching breech plug face will do the job.
I did open the end bore to thread the breech area just like this. Use the thread cutter with the same setup without doing anything to the barrel. Use the drill press as a guide with drill press return spring disengaged and hand thread slowly by turning the drill chuck.
Use plenty of cutting oil.
I squared the barrel off with a disc sander.
Make sure your work mate or bench is level in both axles. I checked with a 4' level.
Picture of setup is here:
http://pedersolilancaster.rsengineering.de/#0.18
It worked good enough to pass the german proof house inspection after completion of the gun. The store bought,pre-threaded breech plug was then hand fitted to the barrel by filing off material on the face of the barrel.
The bottom of the hole need not be square. It only has to match the end of the plug. If the end of the drill has a 30° angle just make the end of the plug to match.
Old time gunsmiths usually had tools made to do the job. OR-- they had lathes.
What is going to happen to that flat shoulder when you run the taps in??? It won't stay very flat will it? I never saw an original muzzle loader pre 1850 that had a flat shoulder in the hole. One consideration is, A flat shoulder is a week point in the barrel. A rounded shoulder is a lot stronger. Some English guns did not have a plug but instead the breech screwed over the outside of the barrel. Manton did this on a lot of his sporting rifles. Just a few ideas. Many gun makers of today are in competition with one another to make the ultimate breech plug. I don't engage in that contest. Logic tells me that if a plug will last 200 or 300 years it's good enough for me.
