How to Avoid a Crooked Barrel?

[daved]

During the course of a recent build, my smith told me that the barrel I had sent him (from a major manufacturer with an excellent rep) was "crooked" - basically not concentric with the bore - at the point he was fitting a brake and thread protector. He explained that this was due to the barrel flexing during turning and was a common problem that didn't affect accuracy. My barrel, however, was more "crooked" than most and this caused difficulty when trying to fit a muzzle device - he could ensure that the device was concentric with the bore but it would not blend in smoothly to the barrel without sanding and shaping the device and end of the barrel. Even then, he cold not knurl the thread protector because of the problem.

I was curious as to whether others with more experience had run into this problem, and more importantly, how I might avoid it in future barrel purchases. Specifically, is it worth ordering a custom barrel to the correct finished length from the manufacturer rather than buying one finished to a longer length from a retailer?

Thanks for any input--

Dave

 

[gunsandgunsmithing]

They're never perfect. I use to believe that ordering a blank of a length to finish at your desired length to be worthwhile...and it may well be, but just the other day I chambered what may have been the straightest blank I've ever seen, and get this...It was a 33" blank!

 

[MDM]

I will preface this by saying I'm not a pro, but I do my own work and occasionally I will do stuff for a buddy if he will keep me company while I do it. Most bore's are never gonna be concentric to the OD of the barrel. He just needs to cut the threads/shoulder/crown concentric to the bore, then dial in the muzzle by going off of the OD of the barrel the last couple of inches of the barrel. Then your brake can be turned down to match the barrel, or even just taper the last 3/8" of your brake down to match the OD of the barrel as the shoulder junction. Basic stuff really. I like the taper on the brake myself. What brake is it? Just buy a knurled thread protector for $20.

 

[Larryh128]

I'm going to agree with MDM, I personally have never seen a perfectly concentric barrel to the bore. Yes, some are very close but not perfect. My personal preference is to turn the brake to about .005 over the OD of the barrel, screw the brake on making sure that it fits perfectly 360 degrees. I then chuck up the barrel with the brake being held in a live center & turn from the chuck to the muzzle using a left hand profiling insert. I only turn the brake and MAYBE up to 2" of barrel depending on how out of round it is. It will always take some polishing to totally blend it in if you don't want a bulge in the barrel. Thread protecters get the same application. Is it totally round? No, but it looks like it is.

 

[fdshuster]

Just out of curiosity: What is the contour? Lightweight sporter, Remington varmint, light varmint or heavy varmint?

 

[jpretle]

I once sent a bbl back to the maker, because I felt it was too far out. No measurements were taken, but looking down the bore, I could not see even the resemblance of a circle. It was more of an oval or parabola.
They sent a new bbl, no questions asked, w/ a $10 bill wrapped around the new bbl.
Guess where I get my bbl's from. Yup, it is that maker.

 

[MrMajestic]

Perhaps you could get a background check done on it to see if it has a record? Sorry, couldn't resist! ;D

 

[daved]

Thanks for all the comments.

-The barrel was contoured to med Palma specs and finished at 30" by the manufacturer.
-The smith chambered the barrel first, cut it for a 24" final length, then threaded the barrel and fitted the brake and thread protector. That's when the lack of concentricity became apparent.
-Cutting the barrel short of its finished length seems to be a factor - as you get farther away from the ends, concentricity increases. So ordering a barrel finished by the manufacturer to the final length should minimize the lack of concentricity, at least at the muzzle.
-The smith did an exceptional job fitting the brake - it obviously required more work but the result is good.
-I haven't checked the thread protector that he also fitted - but its function is only to protect the threads so no biggy.
-Since the lack of concentricity apparently doesn't affect accuracy, and he could fix the disparity with a little extra work = no need to trash/exchange the barrel. Not certain that contacting the manufacturer might not have been a good idea. The smith didn't mention it and I trust his expertise. I'll probably give them a call just for curiosity.

Thanks again,

Dave

 

[spclark]

The nature of machining rifle barrels being what it is, if you want a barrel's bore to be centered up at the ends when finished, you'd best save profiling until just before final chambering and muzzle work.

Cut to rough length first, then carefully profile with bore centered at each end. Drastic shortening of a profiled blank intended to finish to a longer length will tend to show any deviation the bore takes relative to the circumference at the new ends.

The bullets don't care if the bore's centerline's dead nuts concentric with the outside profile, though the barrel's harmonics might need some careful planning when it comes to 'timing' it to your action.

 

[mikecr]

But if the bore holds any stress in it(from rifling) then you need contouring completed before lapping.

 

[spclark]

But if the bore holds any stress in it(from rifling) then you need contouring completed before lapping.

Is this a 'cut vs. button' thing?

I agree to a point Mike, that point being one expects custom (not factory) barrel blanks to be relatively free of stresses from manufacturing.

I'll have to ask some friends in the custom barrel business what their take is on your 'profile before lap' recommendation.

 

[mikecr]

An advantage to cut rifling is that no stress is introduced in that operation . If the barrel itself is also free of stress, then you can turn down a cut rifled barrel any time with no affects to it's bore.
When you turn down a button/broach rifled barrel, the bore opens with this.
It's just opposite with hammer forged(the bore closes with contouring).
So major profiling should be established BEFORE lapping to final dimensions.

You have similar cause/effect with temperature gradients. If I had control over it for a competitive non-cut-rifled barrel, I would also have it taken to competitive temperatures during lapping. But I'm sure nobody does this, and many barrel makers and 'smiths' fail to consider bore changes in any regard.

 

[spclark]

Thanks for the details Mike. So the takeaway on this is, if you expect a quality barrel with 'centered' rifle bore at both ends you'd best order a profiled blank that's close enough to your desired finished length without having to cut off too much on either end during the fit & finish stages?

 

[mikecr]

I think that & offer another $50 to have the barrel maker spin a few and send one that turned out centered very near your finished length.

I know barrel making is a big investment, but I don't see R&D efforts from any of them. If there were, then by now someone would produce, cull, & sell better barrels than others. Apparently it just isn't happening.
If you do run across a barrel maker who will hear you, then I'm sure you could explain your need and solicit his help. Who better than the guy that chooses your barrel?

 

[Erik Cortina]

I think that & offer another $50 to have the barrel maker spin a few and send one that turned out centered very near your finished length.

I know barrel making is a big investment, but I don't see R&D efforts from any of them. If there were, then by now someone would produce, cull, & sell better barrels than others. Apparently it just isn't happening.
If you do run across a barrel maker who will hear you, then I'm sure you could explain your need and solicit his help. Who better than the guy that chooses your barrel?

Is there any data backing up your theory that barrels that are ordered close to finish length are more concentric? If so, how do they get the beginning and the end of the bore straight, but put a dip in the middle?

As far as the extra $50, do you think barrel makers will jump extra hoops for someone? They are swamped with work as it is, I doubt they would like to add complexity to their process.

If you want a perfectly concentric barrel, order a straight contour blank and turn it between centers in a CNC lathe to the profile of your preference.

 

[mikecr]

Hard to drill a straight 32" hole.
The deeper the hole the greater the wander, and there could be any abstract to it. So a centered bore, breech to finished end, would likely have to be found in the process (rather than produced).
But it could be done,, a lot of things could be done.

It's a matter of finding a barrel maker who would.
Erik's right though, in that it would not be easy today.

 

[Hal]

Some barrel makers contour before drilling and then drill from the muzzle end.

Hal

 

[dmoran]

Mike -

In no way a fact here, just saying as input... but the best barrel (raw accuracy wise) and that I felt was a "hummer", that I've ever owned, definitely did not have a straight-bore, and actually is one of the worse barrels I've ever owned in terms of being straight.

A gunsmith named Jerry Simison once told me a similar story of one of the better 6PPC barrels that he used in 100/200-BR, and how bad bent it was.

To another aspect, I am a firm believer in barrel indexing and fitting the barrel to an index.
A couple years back I did some"spin testing" at both 100 and 400yds with 4 different barrels, that showed me strong proof that indexing can be a very relevant aspect to precision accuracy.

Interesting input... Thanks
Donovan

 

[MClark]

We ( I work for Dave Van Horn) do a lot of cut and thread jobs for brakes and suppressors. Nearly all when cut to 16-18 or so on suppressor jobs the bore is way off center. I cut the threads with the bore centered and it will leave an uneven shoulder.
We give the customer the option of contouring the barrel and blue to make it even or leave a step to the brake large enough to hide it. No one wants to pay for it.
With a new barrel we cut to just over finished length and contour on centers.
We make our own blanks and sometimes they do not drill straight, those are either redrilled large enough so the drill does not follow the hole, like 20 gauge, or are cut up and used to make brakes.

Mark