Dialing in a barrel for theading

[COMachinist]

I saw a video on threading a barrel 5/8-24 for a tunner brake. The person was using dti with a long "80mm probe" inside of the bore. Does this sound like a good way to dial in the run out? I would think this would change the scale of deflection at the dti. What say you gun smiths?
CH

 

[MrWhoopee]

I'm no gunsmith, but you're not looking for actual measurement, you just want to get to zero.

 

[GeneT45]

It would be interesting to see the setup described, but a brake (or other muzzle device) is pretty easy, and pretty forgiving. I'd just slip the best-fitting deltronics pin into the bore, indicate it true, and go.

As @MrWhoopee said, the exact value is irrelevant, you just want 'zero'.

GsT

 

[silverhawk]

I would get a piece of rod to match the barrel bore, set that in the barrel protruding out, and work off of that. Barrels are usually rifled, and I'd not want to get mixed up on whether a DTI is in a rifling groove or not.

If using a DTI, you can set the tip at an angle appropriately if you don't care about the rifling and you use the inside. If you can't get a good angle with the tip, you will end up with cosign error, meaning the DTI won't be as accurate.

The rod trick gives a surface you can also use, making sure you get it lined up the right way.

Sent from my SM-T500 using Tapatalk

 

[pontiac428]

An indicator is called an indicator and not a gauge for a reason. The method you describe is probably the most common among gunsmiths, but reading among the lands and grooves is a pain that takes practice and patience. The rod method is much easier, but there are reams of debate written for and against it all over the interschweb that you can spend the rest of your life trying to parse. Luckily, once your barrel device is threaded on, whatever affect it has on ballistics is locked and consistent. So dial your barrel to your level of comfort, it'll come out fine in all likelihood. It's chambering you should really take pains over anyway.

 

[COMachinist]

Yea I know what an indicator is, hence dial test Indicator. With an 80mm pin length, would it hardly move the dial enough, to get down to a few 1 tenth
TIR. He had it monted to a holder in the tail stock, strait down the bore. You could see the lands as he turned it by hand in chuck. The video showed the face of the indicator and it look to be less than a 1 tenth, but was it realy or really 1-2 thousandths run. I don't want to get a baffle strike on my new supressor.
CH

 

[mickri]

I can't give you any suggestions on how to do this. But I would like to see some pictures on your set up.

 

[derf]

You don't need a long probe or a tight fitting rod. I use a spring loaded center and indicate off it.

 

[BWS Arms]

Turn a snug fitting pin and indicate off it.

 

[pontiac428]

If you're really concerned about concentricity, put the barrel between centers and cut your tenon and threads that way. Then put it in a steady and touch up your crown. Production barrel crowns leave a lot to be desired anyway; the miniscule retouch will probably help accuracy in most cases. I have done this many times. Just go real easy on the quill pressure when using centers. There are many ways to skin this cat.