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How best to bore a tapered hole in steel?
Trying to match the taper of a civil war cartridge (Burnside) in the breech block.
Lathe plus boring bar or ...?
Lathe and a boring bar sounds good.
or, make a tapered D-reamer.

Do you have a taper attachment?

I made some SB spindle adapters with a MT3 hole and ended up boring the hole. I used a very sharp bit on the end of a 3.5" hang boring bar, fine feed and medium speed. I had to run a couple of spring passes because of the overhang and small OD boring bar. It took a while, but the results were very good - a MT3 center stuck like glue.
Paul, were you able to find any dimensioned drawings for this? Just wondering if you are wanting to duplicate the original breach block dimensions, or are you sizing it to fit modern day replica cartridge case dimensions? I've read that the newer cases with a flat bottom on them are too long to chamber in original breach blocks, as oppose to cases with the dished bottom for the flash hole.
Will be using repo cartridges with the dished bottom like the originals, so it looks like the original chamber dimensions would work.
I have some scaled cutaway drawings for the breech block but haven't measured them yet, and also some brass repo cartridges, a!so not measured.yet.
Still in the planning stages right now.
Sounds good. Tom's idea of making a D-reamer might be the way to go since you have casings to work from already. That way you can make test cuts with the reamer in scrap stock first to check the fit.
Not that familiar with D reamer construction though i have heard of D drills.
How would one make the reamer?
Same as a drill. Just turn the profile and mill or grind a flat to the center line.

That sounds logical and simple.
Presume you use drill rod and harden it?
Also step drill out most of the hole before reaming?
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