Gunsmithing Barrel Setback Question?

[vonbalkenbush]

Here's the question. My 6XC was chambered on a buddies lathe. He does a bunch of local bolt guns for hunters, quality is so-so. The reason I went with him is one, because he basically traded me out and it was on the cheap, and two I got to watch from start to finish.

He indicated the barrel in for chambering from the outside diameter of the bore to within about .0005"'s. Luckily it was a Bartlein and they're very dimensionally consistent. I was less than pleased with this, but it still shoot's in the .3's and .4's at 100 yds most of the time and is good enough for me at this point.

My question is, when I set the barrel back, and have it indicated in properly the next time, will the reamer follow the old chamber which was cut off of his lazy measuring from the OD of the bore or will it cut a new path?

If it won't cut a new and true path, how much of the chamber end will I need to hack off to get it cut straight on the second go around?

-SBS

 

[Frank]

Re: Barrel Setback Question?

Well if you cut off enough to get back to the bore, then that wouls do it.

 

[RADcustom]

Re: Barrel Setback Question?

Are you staying with the same caliber? Did he use a floating reamer holder?

Dial in the bore and check the run out of the chamber and the threads.

If you are not happy with the results, cut off the threads. Cut a new tenon and bore the chamber to center everything up for the new chamber.

 

[my human host]

Re: Barrel Setback Question?

Is that half thou indicated or actual runout?

 

[vonbalkenbush]

Re: Barrel Setback Question?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RADcustom</div><div class="ubbcode-body">Are you staying with the same caliber? Did he use a floating reamer holder?

Dial in the bore and check the run out of the chamber and the threads.

If you are not happy with the results, cut off the threads. Cut a new tenon and bore the chamber to center everything up for the new chamber. </div></div>

Yes I am staying with the same caliber, but it will be a different reamer, not his. I believe it was a floating reamer holder but am not positive. I will call him and ask.

So I am concluding that cutting off the shank should be adequate to give myself a fresh start?

-SBS

 

[vonbalkenbush]

Re: Barrel Setback Question?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: my human host</div><div class="ubbcode-body">Is that half thou indicated or actual runout? </div></div>

That would be a half thou indicated, he never broke out his ten-thou gauges even thou I tried to get him to, as well as his range rods. He said it wouldn't make any difference. He's an older guy, stubborn as a mule and stuck in his ways. I figured if it shot crappy I'd lose an inch of barrel and it started at 27" anyway. Like I said, it was a good learning experience, and now I know of a bunch ways I will not do things LOL.

-SBS

 

[RADcustom]

Re: Barrel Setback Question?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SagebrushShooter</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RADcustom</div><div class="ubbcode-body">Are you staying with the same caliber? Did he use a floating reamer holder?

Dial in the bore and check the run out of the chamber and the threads.

If you are not happy with the results, cut off the threads. Cut a new tenon and bore the chamber to center everything up for the new chamber. </div></div>

Yes I am staying with the same caliber, but it will be a different reamer, not his. I believe it was a floating reamer holder but am not positive. I will call him and ask.

So I am concluding that cutting off the shank should be adequate to give myself a fresh start?

-SBS </div></div>

Fresh threads that are concentric with the bore will be the first step in the right direction. That amount should give you enough fresh material to correct any mess ups if they aren't grossly misaligned.

 

[vonbalkenbush]

Re: Barrel Setback Question?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RADcustom</div><div class="ubbcode-body">

Fresh threads that are concentric with the bore will be the first step in the right direction. That amount should give you enough fresh material to correct any mess ups if they aren't grossly misaligned. </div></div>

I don't think it's grossly misalighned, just a little, but that's enough for me to want to do it right when the opportunity arises. I'm waiting on a reamer and gauges from JGS as my buddy will not loan his out.

Thanks for the help, I'm feeling better about this already. I'll lose a little velocity but the trade off will be the system will be shooting to it's full potential.

-SBS

 

[Rprecision]

Re: Barrel Setback Question?

Boy, thats a raw deal! I would be setting back that .3 gun ASAP.

 

[catskinner]

Re: Barrel Setback Question?

You might just leave it for now. I mean .3 isn't exactly bad. This has to be a joke

 

[2156SMK]

Re: Barrel Setback Question?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SagebrushShooter</div><div class="ubbcode-body">how much of the chamber end will I need to hack off to get it cut straight on the second go around?

-SBS </div></div>

About 1.5" should do it.
Make sure to rough out the chamber with a boring bar as the boring bar will correct any left-over mis alignment after the barrel is dialed back in for the rechamber.

 

[vonbalkenbush]

Re: Barrel Setback Question?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: catskinner</div><div class="ubbcode-body">You might just leave it for now. I mean .3 isn't exactly bad. This has to be a joke </div></div>

No joke. It doesn't shoot in the .3's with any degree of consistency. I've only had two 3 shot groups that did that. Usually 0.5-0.7's are more common for 5 shots. Which is still not bad until you consider the setup and my shooting abilities. I shoot about 400-500 rds/month in precision bolt gun. I have been able to consistently hold .2-.3's in the past when the gun was setup right and conditions are good. This setup is:

Bighorn Tactital SA
Manners T5A w/mini chassis
Bartlein 7.5" twist m40 contour
Jewel Trigger
Premier 5-25x56

This setup should be capable of out-shooting anything I've had previous which have mostly been trued up 700's. I probably won't re-do the chamber until I've put a few more rds down it. But it should be performing better for what it is. Only thing that I didn't do right was wait for the right smith, I got impatient as I've been working on this build for 1.5 years getting parts and waiting on funds. I skimped at the last second, learned my lesson.

-SBS

 

[vonbalkenbush]

Re: Barrel Setback Question?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 2156SMK</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SagebrushShooter</div><div class="ubbcode-body">how much of the chamber end will I need to hack off to get it cut straight on the second go around?

-SBS </div></div>

About 1.5" should do it.
Make sure to rough out the chamber with a boring bar as the boring bar will correct any left-over mis alignment after the barrel is dialed back in for the rechamber.
</div></div>

That sounds about right. Hadn't thought about the boring bar, that should fix it up nicely. Thanks for the advice, it is very much appreciated.

-SBS

 

[my human host]

Re: Barrel Setback Question?

I'm thinking there's more to it than .00025 runout in the chamber/threads. Sub half moa should be no problem, even with the runout.

It may well be that the setback will resolve your troubles, but there's more to this than the runout alone.

I'm not doubting your credentials or your word. Just speaking my mind.

 

[vonbalkenbush]

Re: Barrel Setback Question?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: my human host</div><div class="ubbcode-body">I'm thinking there's more to it than .00025 runout in the chamber/threads. Sub half moa should be no problem, even with the runout.

It may well be that the setback will resolve your troubles, but there's more to this than the runout alone.

I'm not doubting your credentials or your word. Just speaking my mind. </div></div>

I think there is probably a lot more runnout than .00025" in the chamber and threads. Where did you get that number from? As I said previously, when he indicated it in it was done with a one-thou dial indicator, not a ten-thou indicator. And it was indicated just under .001" to OD of the bore. I know that much cause I watched him do it. That would lead me to believe there's room for a lot more runnout than .00025".

I haven't shot a ton of paper with it to be honest. It was only the first two weekends I had it out. It turned in a couple of nice three shot groups in the .3's during barrel break-in. Following week I had three 5 shot groups that ranged from .4-.7 CTC. That was the last time on paper.

I've had it out to 1200 yds on steel, it shoots pretty good, I just feel it should shoot better for what it is. I know it might sound arrogant, but it ain't me. I'm shooting another steel comp with it this weekend, I'll put it on paper after the match again. Thanks for the input.

-SBS

 

[my human host]

Re: Barrel Setback Question?

SS,

When I read your first post, I interpreted it to mean that the indicator was showing .0005 variation as the barrel was rotated in the lathe. In reality, this means you need to adjust the barrel half that amount in the appropriate direction to get it spinning true. That's how I came up with the .00025.

Most of us strive to dial them in better than that, but it's probably not enough to cause any real problems.

I understand your desire for perfection, though.

 

[Edo1]

Re: Barrel Setback Question?

At what point do you feel the runout is acceptable?

 

[my human host]

Re: Barrel Setback Question?

Anything around a ten thousandth works for me. I didn't dial them that tight when I first started and the rifles still shot really well.

I have better equipment now.