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A friend asked me to put threads on the end of an octagonal barrel to mount a suppressor. I plan to use a four jaw chuck and indicate off of a dowel pin in the bore.
I was wondering about what I should do to the crown. Leave it alone or maybe square it up?
Thanks
Is there enough metal for the suppressor to still shoulder well once threaded? I ran into that issue when trying to thread and older Contender octagonal barrel. Something large like a Henry barrel should have plenty of metal left.
I would square up the crown while you're there doing it.
Lightly square the crown this will give a solid zero ( especially if you have a dro) to work from. Then when done put a nice crown on the muzzle. If enough room you could even recess it a little. this would give a ring to set and square the suppressor.
I have threaded a lot of barrels for suppressors. I am assuming you have a hollow spindle on your lathe. I make a wood plug that is a bit undersize of the ID of the spindle and drill a hole through the center of the wood plug that holds the breech end of the barrel. The pin in the bore is a good idea to center the barrel. The wood spindle plug keeps the barrel from wobble. When you turn the major diameter for your threads your threads will be dead nuts center. While you are all centered up you should recut a nice crown.
I always crowned octagons just like normal barrels after threading. 11 deg. cut then a ever slight chamfer to break the edge of the rifling to prevent cleaning rod damage. And yes, 4 jaw chuck and indicate the bore with a gauge pin. And an aluminum ring to center the breech end in the spindle bore as Rockindaddy mentioned.
If it's already crowned I'd leave it alone. If not, generally I'll just do a 11 degree crown and leave a nice flat. I'd also make him a timed octagon muzzle thread cap for when the suppressor isn't in use as the sharp 90 on the ends of the flats will want to cut whatever they contact. To prevent that on the cap, bevel the corners until you hit the center of the flat and they no longer feel sharp.