Bore diameter changes when turning down muzzle end?

[Rustystud]

Over the last 20 years I have chambered, cut and crowned over 10,000 barrels. Some were hunting rifles some were target rifles. I never part off muzzles. I always cut them on a band saw. If you part off a muzzle you can't start a piloted cutter down the bore. It is not just the edge, it effects, the bore a 1/2" or more. If you were to look at the metal under a microscope you would be able to a change in the metal grain structure. The bandsaw blade is only .065" and I run cutting oil to lubricate and cool the sawing action. I still open up the bore with a kiss from a 60 degree cutter. Then I crown with a piloted 11 degree cutter run at 55 rpms and flood coolant. Then I polish finish with 320 grit, 600 grit, and 800 grit.

 

[Dusty Stevens]

Over the last 20 years I have chambered, cut and crowned over 10,000 barrels. Some were hunting rifles some were target rifles. I never part off muzzles. I always cut them on a band saw. If you part off a muzzle you can't start a piloted cutter down the bore. It is not just the edge, it effects, the bore a 1/2" or more. If you were to look at the metal under a microscope you would be able to a change in the metal grain structure. The bandsaw blade is only .065" and I run cutting oil to lubricate and cool the sawing action. I still open up the bore with a kiss from a 60 degree cutter. Then I crown with a piloted 11 degree cutter run at 55 rpms and flood coolant. Then I polish finish with 320 grit, 600 grit, and 800 grit.

How about when turning them down?

 

[Rustystud]

Anytime you see colored chips coming off your tooling you are having and affect on the surounding metal.

 

[Dusty Stevens]

Anytime you see colored chips coming off your tooling you are having and affect on the surounding metal.

So have you seen a bore open up after threading the muzzle? Thats what the OP was wondering here. Not sure if youve ever checked with pin gages or not. I have some deltronic pin sets and they do indeed open up

 

[LVLAaron]

^ - I like the polished inserts meant for aluminum when doing crown work. They're razor sharp and don't need a lot of cutting pressure. They're also super cheap, so use'm a couple times and toss them.

I have a couple of premium cut rifled barrels that are threaded...(I didn't thread them, they could have been done at 2000rpm dry on a cnc) I can take a gauge pin that fits nice on the muzzle end... it'll slide in almost exactly to the shoulder of the thread.

 

[SKWERLZ]

E

So have you seen a bore open up after threading the muzzle? Thats what the OP was wondering here. Not sure if youve ever checked with pin gages or not. I have some deltronic pin sets and they do indeed open up

Especially cheaper button rifled barrels.
Lots of internal stress in those.

 

[SKWERLZ]

^ - I like the polished inserts meant for aluminum when doing crown work. They're razor sharp and don't need a lot of cutting pressure. They're also super cheap, so use'm a couple times and toss them.

I have a couple of premium cut rifled barrels that are threaded...(I didn't thread them, they could have been done at 2000rpm dry on a cnc) I can take a gauge pin that fits nice on the muzzle end... it'll slide in almost exactly to the shoulder of the thread.

Interesting
I have a few of those inserts (fantastic for cutting custom wood fly rod reel seats) and will try them on a crown.

 

[Dusty Stevens]

Interesting
I have a few of those inserts (fantastic for cutting custom wood fly rod reel seats) and will try them on a crown.

If itll cut your finger itll be perfect for a crown

 

[LVLAaron]

Sharp as a cats claw. I use these for crowns and to "pre bore" chambers. Use rubbing alcohol as a lubricant and you'll get an unbeatable finish.

 

[GunDoc]

For Optimal Accuracy with Threaded-Muzzle Barrels, Use Larger Muzzle Thread Diameter « Daily Bulletin

Our friend Robert Whitley of ARX Enterprises LLC has learned, through careful measurement and testing, that some barrels threaded 5/8 x 24 TPI at the muzzle may not deliver optimal accuracy.

bulletin.accurateshooter.com

 

[Dusty Stevens]

Sharp as a cats claw. I use these for crowns and to "pre bore" chambers. Use rubbing alcohol as a lubricant and you'll get an unbeatable finish.


View attachment 1417084View attachment 1417086

Whats the number on your toolholder?

 

[LVLAaron]

"CHINA"

I have various sizes of these solid carbide boring bars. They're super ridgid and cheap.

SOLID CARBIDE C06K-SCLCR06 INDEXABLE LATHE BORING BAR 6 MM SHANK | eBay

• Shank length: 125mm. • Wrench: T8.

www.ebay.com