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Gunsmithing button rifle barrel mystery.. anyone want to weigh in

S

squib-load

Private
Full Member
Minuteman
Mar 11, 2017
143
34
#1
I bought a 6.5 caliber remage barrel from a quality manufacturer of button barrels.

it was supposed to be a 1/8 twist.

after trying to break the barrel in it was not shooting well... and I already had the exact same barrel / caliber / etc from the same mfg just in a different contour

velocity was much slower 150fps slower and needed almost 2 grains more powder to get that velocity back and each charge increment in the new barrel resulted in a velocity gain about half of the velocity increment vs the old barrel..

didn't group.. at all.. a 7 charge ladder at 100 yards through 2 possible 3 known accuracy node velocities .. no rounds closer than .5 inches to each other and the full group over 2" across closer to 2.5"

cleaning the barrel, a bronze brush felt like it was less tight than in my previous barrel the bristles would walk the barrel while it had some push in my old barrel.. its a .25 otis brush and the package says up to 6.5mm.. and have used them on the old barrel just fine.. don't like tight bronze brushes.. i normally don't use the bronze and just use nylon but broke it out thinking that I wasn't getting all the fouling out..

but here is the REALLY interesting part...

it was supposed to be 1/8 .. but taking a nylon brush and a ball bearing rod to several places in the barrel.. it was dead nuts 1 / 8.5 not off by a little.. perfect 8.5 twist.. WTF

now here is the really weird part... the mfg DOES NOT OFFER a 1/8.5 twist in this caliber... they offer 8.5 in 6mm and 7mm but not 6.5... they don't have a 6.5 1/8.5 button?

so HOW THE HELL did this get done..

was this a properly gun drilled and honed 6.5 blank that had a 6.5 cal 8 twist button pulled by a machine set with cams to twist and pull at at 8.5 rate? can you say stress

was it a 6.5 sized barrel that had a 6mm or 7mm 8.5 twist button pulled through it.. since it feels loose it would have to be a 7mm I would think.. as a 6mm button would leave the barrel tight/undersized and its definitely loose.. even more stress on the steel if it was a 7mm pulled through a 6.5?

anyone want to venture a guess on what the hell went wrong here..

the barrel went back... but I just can't get my head around how this could have been done...

moreover.. was it dangerous.. I would think that the additional stresses might compromise the grain of the barrel weakening it significantly ...
 
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#3
Some manufactures index the button as they pull it. Some use a thrust bearing and let the button do what it wants. Both setups work. Every manufacture I've seen has a pressure gage on the hydraulic system to monitor the amount of force required to pull or push a button through. With that being said there is no way anything but the correct diameter button could have been used. Pressure readings and the sound from the hydraulic pump would give it away. Twist rates on button barrels have a +/- tolerance. Wait for the report from the manufacturer.
 
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#4
@DAVETOOLEY

thanks for weighing in...

its definitely not a button slip or anything like that.. its a solid, perfect, 8.5 everywhere in the barrel, muzzle, mid and breech..

and without a 8.5 button in their inventory, the 8 twist button was forced to turn 8.5, slower than its cut /angled for like gears trying to turn at different rates, if the bore was indeed a blank for 6.5.

The CS has been great and they look like they are eager to make it right and tell me, if they can figure it out, what the issue is..

just being a 8.5 twist should not make the barrel shoot this bad, the stability of the bullet on the miller scale is still fully stabilized... and the .5 twist according to tests on barrel twist that I have seen.. should not throw the velocity more that 20-40fps... not 150...

only thing I can think of is that being slightly oversize 'might' cause enough reduction in friction so that the powder never produces enough pressure and does not burn correctly... that might explain the velocity.. and possibly a lot of dump pressure when the unburned gasses ignite as the bullet leaves the barrel.

but at the velocities that the bullets are launching at.. and at 8.5 twist there should still be some node in there somewhere.. but the barrel was all over the place leading me to believe there must be a lot of stress in the steel on top of everything else.

I would think that this mfg uses the latest and greatest tech for button rifling .. its definitely not a cottage industry maker, so being a little off, or letting the button free turn is probably not it.. I am sure they are using machines that precisely control the twist..
 
#5
@diverdon

so you are going with a 8 button in a proper diameter blank.. just with the machine to twist at the wrong rate? that is my thinking as well.. but would that also contribute to the 'loose' bore or are we looking at 2 different dimensions that made it my QC?

turning a modern button where the rifling is angled in the button for the twist its designed for turning at the wrong speed would be like gears binding trying to turn at different rates I would think the barrel steel and not the carbide button or tooling would yield.. and absorb that torque

this is a 26" barrel so probably buttoned at lest 27" blank.. possibly longer.. that extra .5 twist would translate to what like 2 additional turns that the button wanted to make where the machine held it back
 
#7
or said another way.. if you were looking at a 8 inch spring and the coils were the helix that the button should follow. stretching the spring to 8.5 inches would be the angle change the button would have to impart vs what its cut for
 
#9
Not to be too obvious but the barrel might have been switched out for a low quality barrel of another make. I have seen some fairly well marked fakes. Once purchased a quantity of Krieger’s out of Alaska.
They were button rifled fakes.
 
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#12
You're probably alright on the drive side of the groove just a little more clearance than needed on the 8.5 vs 8, the trail side depending on their clearance may have dragged a bit. You might be able to detect it with an eyeball inspect, the geometry might look a bit squint. The standard tolerance variance of twist is usually +/- .125". Rather than checking full revolution, also go half revolution or even 25%, or heck 200%, or check it from muzzle to chamber as well as chamber to muzzle. Just in case the twist isn't uniform.
Depends on the tool geometry whether it's that big of a deal an 8 twist button was pulled thru at 8.5 twist. How would people button gain twist barrels otherwise? All in the angle of the dangle.
 
#13
thanks JR .. no more testing for me.. its back with the Mfg, they will have it tomorrow.. so now its up to them to tell me what is what..

by the by.. I didnt think anyone was making gain twist button rifles.. thought that had to be cut rifeling hence one of the selling points of a kreiger or the like..

thanks for weighing in...
 
#17
GH41 said:
How in the hell can you make the button gain twist? I am having trouble wrapping my head around it.
Click to expand...
Ha..spin the tool or the barrel a little faster at the end, basically. Tool has to be right for it. Now the real zinger is who makes handlapped gain twist barrels?
 
#19
well the mfg says that the twist is correct.. still don't know how I could pull a nylon brush backward through the barrel... 6 times.. 2 from the muzzle for 1 turn, 2 from there and 2 more times near the breach.. and all 6 times come up with balls on 8.5.. and do the same with my old barrel and get balls on 8.. but they said they used a machine that works with a lead lap and its right..

the bore/chamber dimensions they claim are spot on and very uniform and contricit.. but both the land and groove diameter are almost a half thou over spec.

for a 6.5 the specs should be .256 and .264.. and this barrel is .2564 and .2644 ... and melonited which reduces friction they also didn't mention if there is some tightening at the bore which helps accuracy

.. so I think that is likely the biggest culprit in my velocity and grouping issues... the RDF bullets run slower than AMAX that I did in a side by side comparison with the old barrel.. by almost 100fps.. and this barrel is 100-150 fps slower than that barrel with the same powder load and RDF 140... most say the RDF bullets are slower for them as well...

so slow bullet (soft, short bearing surface, whatever) in a slow barrel that is half thou oversized is looking like the culprit not getting the R26 powder enough pressure to burn correctly.. as the fouling and unburned kernels are a dead giveaway ...

they spent 2 days doing measurements.. and monday they are going to put it in a test action and run some index loads though it to get addl. data.
 
#20
Your nylon brush was most likely not following the rifling and was skipping over lands. The manufacturer's method for checking twist rate is surely more accurate. Sounds like you are getting above and beyond customer service from that barrel maker. Most would not have gone to that much effort to check a returned barrel.
 
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#21
I agree; sounds like they are doing a great job to make sure you have a good tube. You should post up the barrel maker... although I assume it’s “brand X” ;-)
 
#22
squib-load said:
well the mfg says that the twist is correct.. still don't know how I could pull a nylon brush backward through the barrel... 6 times.. 2 from the muzzle for 1 turn, 2 from there and 2 more times near the breach.. and all 6 times come up with balls on 8.5.. and do the same with my old barrel and get balls on 8.. but they said they used a machine that works with a lead lap and its right..

the bore/chamber dimensions they claim are spot on and very uniform and contricit.. but both the land and groove diameter are almost a half thou over spec.

for a 6.5 the specs should be .256 and .264.. and this barrel is .2564 and .2644 ... and melonited which reduces friction they also didn't mention if there is some tightening at the bore which helps accuracy

.. so I think that is likely the biggest culprit in my velocity and grouping issues... the RDF bullets run slower than AMAX that I did in a side by side comparison with the old barrel.. by almost 100fps.. and this barrel is 100-150 fps slower than that barrel with the same powder load and RDF 140... most say the RDF bullets are slower for them as well...

so slow bullet (soft, short bearing surface, whatever) in a slow barrel that is half thou oversized is looking like the culprit not getting the R26 powder enough pressure to burn correctly.. as the fouling and unburned kernels are a dead giveaway ...

they spent 2 days doing measurements.. and monday they are going to put it in a test action and run some index loads though it to get addl. data.
Click to expand...
Don't get too hung up on the .2564/.2644..it's not half thou oversized, that is well within 6.5 accuracy standard tolerance depending on the bullet. So did you measure the major diameter of the bullets?
 
#23
I don't have a mic that is accurate below a thou.. but over on another board a guy mic'd a couple berger, hornady and the RDF.. the RDF was the only bullet below .264.. at .2638.. so the bore is over by 4 tens and the bullet under by 2 tens.. so stacked that is 6 tens which is actually over a half thou... I am thinking this is the most likely culprit.. combined with the slickness of the melonite.. the powder is not building the proper pressure as it did in the tighter stainless barrel.
 
#24
Bore drives the bullet, doesn't affect pressure much as does affect jacket if too thin but can help accuracy. Groove drives the pressure based on throat, so you gotta look at those two things there for velocity. Cross section also important and probably still well in the ballpark. If the melonite reduces the friction it will reduce the velocity much like moly, which is a good thing you can add more powder for better case fill. I'm saying don't just label a .2644 groove as a non shooter, even with RDF, because there's more to it than that.
 
#27
If you only tried RDF's and no other bullet type through the barrel I think you need to broaden your test. RDF's are reported by many people to have worse accuracy than Sierra MK's, Hornady ELD's, and Berger Hybrid's.
 
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#28
same barrel mfg, my old barrel from the same company, just in a much lighter profile, same twist (supposedly) just tighter bore.. shoots these into .25" bugholes...

satterlee uses RDF bullets as well with R26 in his accuracy addiction 6.5 with equally impressive results...

slapped the old barrel back on the action.. and even though it was completely cleaned for storage.. the first 5 shots... 3 were at .29 group and the extreme spread was .67 to include the CB shot... I would say that the bullets work as advertised when shot though a bore of the correct dimensions.
 
#29
squib-load said:
same barrel mfg, my old barrel from the same company, just in a much lighter profile, same twist (supposedly) just tighter bore.. shoots these into .25" bugholes...

satterlee uses RDF bullets as well with R26 in his accuracy addiction 6.5 with equally impressive results...

slapped the old barrel back on the action.. and even though it was completely cleaned for storage.. the first 5 shots... 3 were at .29 group and the extreme spread was .67 to include the CB shot... I would say that the bullets work as advertised when shot though a bore of the correct dimensions.
Click to expand...

RDF's are really finicky and inconsistent. Lots of reports of the RDF's producing random fliers. For me, they would occasionally shoot tiny 3 shot groups, but never a 5 shot group under 1 MOA. Meanwhile it doesn't take much to get Berger Hybrids shooting 1/4 MOA.

Take what sponsored shooters say with a grain of salt. Whenever someone recommends a product, I like to know what angle they are coming from, rather than taking the endorsement for face value. Lots of sponsored shooters will blatantly push a product from a sponsor, even if it doesn't fit your purpose or work as advertised.

I find that the sponsored shooters in the precision rifle community are notoriously bad for whoring themselves out to companies, and blindly recommending their products. Then the next year they are sponsored by completely different companies, and all of a sudden their products are now the best thing ever and they "couldn't have won the match without product X". That shit gets old quick.

There are whole threads dedicated to RDF's and their piss poor performance all over multiple precision rifle boards. Test out some better/more consistent bullets before you completely write off that barrel.
 
#30
I will say.. in full disclosure that I absolutely agree with you on the RDF in 308.. I bought 2K and they are terrible.. in one lot.. there are a mix of bullets that have misshaped ogives.. if you check the base to 308 ogive they look about right.. but if you take gradually smaller caliber comparators and go up the nose.. they are different by .010".. I shit you not.. and they group like shit...I chased my tail with them on a new schnieder 308 barrel and it drove me nuts.. went back to my index loads of 175SMK and right into .5" groups.. the barrel even shoots the TMK well.. yeah.. no love for the 308 RDF.. the other lot is all the one shape.. so they caught it eventually but they were all the 'bad' shape so they were a bit more consistent as at least you could seat them to the same depth give or take but they have too many other issues.

the 140 on the other had seemed solid.. the measurements I could make seemed consistent and again.. the sporter barrel ate them up and spit them into really nice groups..

also agree that berger has shot 'mostly' better in all my rifles but at twice the price.. and the full VLD seem even more finicky than the RDF.. the hybrids are a bit easier.. same hybrid ogive that the RDF uses..
 
#31
If they work for you then have at it. I have a bunch of 140 RDF's sitting in my reloading room now relegated to barrel break in, fouling rounds and barricade practice. Can't get them to shoot for shit in my 6.5 creedmoor. Which is a real shame, as they have a great BC are a great price, was really hoping to get them to work.
 
#32
I am betting that those that are having issues with the 140 RDF might be stemming from the .2638 diameter vs .264 to .2642 diameters of hornadys and berger..

my hunting weight barrel that shot it well was noticeably tighter with a bronze brush than the current 4 tens over of the current barrel.. the bristles walked the barrel vs the typical push that I got in the old barrel..
 
#33
the RDF were 100+ fps slower in the old barrel than some 140AMAX bullets that I got with the purchase of the rifle.. loaded them with the same load of r-17 so even in the tighter bore they shot noticeably slower..
 
#34
Every barrel is different. Try a different bullet if the manufacturer sends the barrel back to you. Otherwise, keep buying barrels until you find one that shoots your bullet of choice the way you want.
 
#36
well the mfg shot some index loads through the barrel in a known action and fixture, and it shot like shit for them as well...

oddly, the first 3-5 rounds from the cold/clean barrel grouped at .5" then opened dramatically over the next rounds.. he offered his personal apology as given the dimensions and other tests on the barrel he know of no reason why it should not perform..

the customer service has been fantastic and they asked if I would like a refund or to have them spin another barrel.. as he is certain that this is a fluke and I agree.. records have been set with this companies barrels so I am sure I have just had a bad patch of bad luck and if the barrel gauges out in all respects... if the issue is a bad heat treat of the blank or some other defect out of their control that is not gaugeable like a stress pocket in the steel.. I certainly don't hold this against them and only hold up their fantastic customer support so I will certainly trust this company to spin up another .. I am sure it will be a shooter..

at least them shooting it confirmed the issues and took the bugger hooking trigger puller out of it (me) and my particular load since they shot some know index loads ...

thanks all for weighing in... I am likely not going to post more here unless anyone following the thread wants me to keep it up....
 
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#37
squib-load said:
well the mfg shot some index loads through the barrel in a known action and fixture, and it shot like shit for them as well...

oddly, the first 3-5 rounds from the cold/clean barrel grouped at .5" then opened dramatically over the next rounds.. he offered his personal apology as given the dimensions and other tests on the barrel he know of no reason why it should not perform..

the customer service has been fantastic and they asked if I would like a refund or to have them spin another barrel.. as he is certain that this is a fluke and I agree.. records have been set with this companies barrels so I am sure I have just had a bad patch of bad luck and if the barrel gauges out in all respects... if the issue is a bad heat treat of the blank or some other defect out of their control that is not gaugeable like a stress pocket in the steel.. I certainly don't hold this against them and only hold up their fantastic customer support so I will certainly trust this company to spin up another .. I am sure it will be a shooter..

at least them shooting it confirmed the issues and took the bugger hooking trigger puller out of it (me) and my particular load since they shot some know index loads ...

thanks all for weighing in... I am likely not going to post more here unless anyone following the thread wants me to keep it up....
Click to expand...
just let us know how the replacement performs
 
#39
So they never told you what exactly the cause was, huh?

FWIW, I have an AR with a 20" 6.5G barrel, cut rifled, and I'm positive it's 1/8.5 and it's my most accurate barrel by far, consistent .33MOA with the right handloads (100gr. AMAX and 120gr. Nosler BT's). The wrong ammo and it's barely a 1-1.5MOA barrel, so it's VERY ammo picky.
 
#40
still testing.. but no, given the gauging and measurements and testing done to date, nothing tells them the barrel should not be a shooter.

the index loads evidently not my load, he didn't tell me exactly what it was other than it was not what I was using.. and not unusual since R26 and RDF are new to the 6.5 norma party. The owner and several other guys there shoot this caliber in F class and have lots of experience on the caliber and make a good deal of these barrels in that caliber so I am trusting that their index load is like the FGMM of 6.5 norma, works well just about everywhere.

what was strange with this barrel is that regardless of ammo, I have never had a cold / clean barrel where the cold bore shot was the fastest and tightest group with subsequent shots getting slower and looser..

my bet is now on stress in the steel from either a bad head treat somewhere in the process or their melanite contractor got the barrel out of temp spec during the hardening. or the over size bore is expanding at a greater rate then normal during heating due to stress and it gets real loose real fast.. but I don't think that they could have caught this one before the barrel left their facility short of shooting the barrel...

they are going to continue the post mortem on the barrel as the new barrel is spun up, and the barrel is already being made and put into the head of the queue and I didn't ask and specifically said, don't have to rush.. evidently its going to be 'hand walked' to each stage and gauged continually during the process.

again... customer service is unbelievable .. could not rate it higher.
 
#41
The 'pickiest' barrels I'd been around, picky for groove dimension, was the 7.5 Swiss. Well, those and bore riders. The swiss shot a conical bullet which formed the parallel on the back end of the bullet and yeah you had to be just so. Just strange that this RDF would be that finicky in a barrel which meets SAAMI spec, since many of these ammo companies run EPVAT and accuracy barrels that match your current bore/groove spec.
 
#42
@__JR__ don't think that this is an RDF issue 'completely' since the mfg did index loads using a different bullet and it shot crazy for them too..

dimensionality and melanite may be playing a part but at this point I am willing to be that it either wasn't heat treated right or the steel is flawed...
 
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