Dialing in a Barrel

[Hamo]

Hi
Long time "hobby" machinist, but never chambered a barrel

From what I understand there are 2 common ways to chamber a barrel - between centres and through the headstock. My lathe is too short for between centres, which leaves me with the second option - through the headstock. I really feel that between centres for me would be a better way to go (just seems to make more sense in the setup for me). I appreciate that everyone has an opinion on what is better, but I'm just trying to get a chamber that shoots OK and is safe. Not after heavy gun precision here.

I have seen a lot of different ways to dial the barrel in this way, including:
range rods (or indicator rods)
Indicating directly on the lands/grooves
Indicating off the outside of the barrel (don't like this option - who knows if its true to the bore)

A lot of the text/videos i have watched say to indicate off the breech end of the barrel, and a few inches inside it (or alternatively with the range rod, to indicate at 2 places on the rod). Everyone seems to say to avoid using the bore at the muzzle to dial in. I realise the bore of a barrel isn't perfectly straight - but I would have thought a match grade barrel would be close - close enough that dialing in over a few inches would be too short to show significant deviation. Also, i would have thought that dialing in the muzzle would effectively be the same as puting the muzzle between centres and chambering it in this fashion.

What would you recommend as the novice "easiest" way to dial a barrel in between centres. I realise that this is a contravercial topic in regards to accuracy, and don't want to start a debate, just curious as to how you all do it and if there is a way that is easier than others?

Also, what precision is necessary? i have seen from 2 thou to 0.1 thou... I will obviously go for as good as is possible, but curious as to what most would consider acceptable

Thanks

 

[carlsbad]

My favorite is between centers.

 

[Cloudrepair]

Even if it's a hunting rifle I would still dial it in to at least .0002 and I dont understand why someone would say to avoid dialing in the muzzle and breach/throat area?
Other then hard for them to devise a way to, i consider that the best way.

Have you read the (130 page pdf of chambering a barrel) in the advanced gunsmithing and engineering forum?
A lot of good stuff in there.

 

[Riesel]

I would refer you to the PDF in Advanced Gunsmithing and Engineering. 130 ways to look for trouble.

 

[hogpatrol]

 

[boltfluter]

.0002 or better and through the head stock. Just be careful not to bend the barrel.

Paul

 

[ridgeway]

I chamber in headstock between two spiders carefully not to induce bending of barrel. I dial in on grooves at the throat and up as far as I can reach with my long stem interapid. Works for me...opinions will vary.

 

[Hal]

Alex had a video on his web site showing one way to dial in a barrel.

Hal

 

[TAJ45]

A bud who has shot a lot of zeroes, very anal, high energy took a known bbl of known accuracy and intentionally ser it back multiple times. He started around .007" tire, then .005, then.003, then .0015 then .0001. All through headstock.
Iirc the 7 was abt factory., 3 was very good but once under 3, the gain was real but more minimal. Just a fwiw

 

[tobnpr]

I chamber between centers, but....
"Tooling-wise" if you've got a long-stem dial test indicator, seems the easier path is directly indicate at the throat area. If you don't, then a rod would seem to be the way to go.

You've not touched on a critical aspect of working through the headstock-which is how you're going to hold the reamer.
This is yet another controversial area, so do your due diligence on this. Needless to say, your tailstock would need to be in perfect alignment in all axes (which usually ain't happening on most machines- even new ones) to be able to hold it rigidly and push with a tailstock. Floating holders, so-called "pushers" and other methods to allow for reamer float.
Good luck, many ways to skin this cat and they can all work well provided the setup is well executed.

Since your headstock spindle bore is large enough, you could still chamber with a steady if you prefer to go that way; just choke up the barrel in a 4-jaw...
Worth considering, since the setup is a lot faster, and while chamber concentricity won't be as accurate as working at the headstock you can still cut a nice chamber this way.

 

[swd]

Since your headstock spindle bore is large enough, you could still chamber with a steady if you prefer to go that way; just choke up the barrel in a 4-jaw...
Worth considering, since the setup is a lot faster, and while chamber concentricity won't be as accurate as working at the headstock you can still cut a nice chamber this way.

If you chamber through the head stock with the muzzle side supported and everything dialed in why would it be any less concentric than between centers?

 

[ridgeway]

There is no reason you can't chamber in a steady as good as you can through headstock.

 

[Hamo]

thanks for all the replies! I hadn't seen the PDF, looks like I have a bit of reading to do. Had a quick skim through. very interesting info there!

A bud who has shot a lot of zeroes, very anal, high energy took a known bbl of known accuracy and intentionally ser it back multiple times. He started around .007" tire, then .005, then.003, then .0015 then .0001. All through headstock.
Iirc the 7 was abt factory., 3 was very good but once under 3, the gain was real but more minimal. Just a fwiw

Thats great info Taj45. I would have thought that .007" of runout is huge and would have broken reamers - I could do better in my 3 jaw self centering chuck I think. Do you know if he was using a floating reamer holder?

 

[TAJ45]

thanks for all the replies! I hadn't seen the PDF, looks like I have a bit of reading to do. Had a quick skim through. very interesting info there!




Thats great info Taj45. I would have thought that .007" of runout is huge and would have broken reamers - I could do better in my 3 jaw self centering chuck I think. Do you know if he was using a floating reamer holder?

 

[TAJ45]

Yes he does. However, he does his trig, drills, prebores, checks tir, final bore and rechecks tir before reaming.
Remember, a reamer follows the pilot hole.

 

[butchlambert]

Yes he does. However, he does his trig, drills, prebores, checks tir, final bore and rechecks tir before reaming.
Remember, a reamer follows the pilot hole.

Clarify that for me. A reamer follows the pilot "hole" or does it follow the prebored hole?

 

[TAJ45]

Prebored. My oops.

 

[Hamo]

Just watched this video of a barrel being chambered

At 13 seconds it shows a barrel dialed in from the breech with a range rod and zero runout.

At 23 seconds, it shows the lathe running with the muzzle and has visible runout.

I figured that the barrel would have a very small amount of bend in it - which is why some recommend centering off the breech end. But the runout at the muzzle is nuts! That barrel would no way sit in the middle of a barrel channel on a chassis. Is this a machinists error, or are barrels really that bent, or am I missing something here?

 

[hogpatrol]

Very interesting. I wonder what brand of barrel.

 

[linebaugh]

Just watched this video of a barrel being chambered

At 13 seconds it shows a barrel dialed in from the breech with a range rod and zero runout.

At 23 seconds, it shows the lathe running with the muzzle and has visible runout.

I figured that the barrel would have a very small amount of bend in it - which is why some recommend centering off the breech end. But the runout at the muzzle is nuts! That barrel would no way sit in the middle of a barrel channel on a chassis. Is this a machinists error, or are barrels really that bent, or am I missing something here?

That is not a machinist error and is common though not typicallly that bad. I don't think it had been brought up but I am planning to build a fixture that will go in the headstock to eliminate the outbound spiders and not induce any barrel bending.
Basically I am looking to take a very heavy wall pipe and add spiders about 6" apart in a rigid mount built to be used in my 4 jaw chuck. I will need to do some testing and see if it can be made rigid enough to support the bbl and keep any movement at zero. Basically to see if I can make it strong enough to be useful. Not my idea but I have seen it many times and am of tbe opinion if it works it could be the best way to chamber. Of course who hasn"t or doesn"t think that?