from 1972 ~ 1976 off and on i worked with Bill Large the master muzzle loading barrel maker.
here is his method which he used on a planer to machine the flats of the bbl. but the same process will work in a milling machine.
1) make yourself a set of 60 deg. centers one rigid the other adjustable with a left hand thread say 3/4"-20 tpi. make it tall enough so that there is 3/8" to 1/2" clearance under the barrel to the table. make it keyed to fit the center t-slot in your milling machine on centerline and make them wide enough to cover the table width allowing for bolt holes to clamp to the ouside t-slots in the table.
on the center t-slot use 1/2" flathead shcs fore and aft to clamp it.
for the outer 2 t-slots make some planer clamps at 3 deg ~ 5 deg. angle screws using 9/16" to 5/8" fine thread shcs or similar long sh set screws radius point not dog point not cup point. make enough planer clamps to clamp every 6 to 8 inches both sides and make the elevation of the screws tall enough to be at the approx. center of the bbl. after you have made your attachments mount them on your milling machine table place the bbl. between the centers and snug up.
mount your planer clamps then scale the distance between the side of your bbl and the screws (which should extend no more than 1/2 the screw dia. out of the planer clamps.) then get some heavy parallel stock in sections long enough to cover the length of the bbl. both sides with approx. 1" gap between the sets of planer clamps which should be equally spaced.
on your first cut support the bbl using adjustble parallels between the bbl. and the table approx. every 6".
make a cut leaving .010" to .020" for finish. rotate the bbl. after this cut clock 45 deg using a 4" combination square head in your 1" gaps check orientation along the length of the bbl. reclamp between centers and clamp planer screws over side parallels again using adj. parallels supporting the bottom of the bbl calculate the differences in cut to support the bbl.
make next cut leaving .010" to .020" for finish.
continue process using sq. head checking 45 deg. and 90 deg. as you go. after all 8 flats have been cut, repeat process machining the final .010" per flat. takes a while but is very rigid and produces a great job if you pay attention to detail and support bbl. snugly every time. you may want to leave a few thou for draw filing and polishing the flats.
you can mount one end higher to make a tapered bbl. or you can shim up 8" to 10" from the muzzle for a swamped bbl.
try it youll like it.
I have a Bill Large barrel on my flinter he made for me in 1964. Then we visited him on a trip in 1969 - he was fooling around getting a planer going.
[This message has been edited by johnoder (edited 08-15-2004).]
that was a little before i met bill but certainly in his prime. im sure your flinter is cutting x's if you can hold it.
bills grandmother mary conly martin and my grandfather charlie conley were brother and sister.that would have made bill and me first cousins once removed he was either 69 or 72 i believe and i was 22 when we met in 1972 he was quite the character wasnt he? i really value the experience that he and others have inspired to followed jim