Proof barrel bored off center

tlsmith22

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#1
My smith just sent me a video of the proof barrel I’m using on my 300 wm build. He was spinning it in his lathe and it appears it is bored around .008 off on the dial indicator. He said its the second Proof in a row from stockys to be bored off center. He didn’t seem very concerned abt it but is that pretty common?
 

tlsmith22

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#5
I am trying but apparently the video format isn’t allowed. It was taken with an iphone. It says the uploaded file does not have an allowed extension.
 

AIAW

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#9
Damn, this sucks because I heard the same thing recently from an extremely reliable source. Heard they were changing a few practices internally to speed up production. Changes... you wouldn't particularly like in a barrel.
 

Bobkittjc

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I did one a couple months ago on which the carbon wrapping was not concentric to the point that the barrel was obviously wobbling when turned between centers. I was not impressed, especially considering the outrageous cost. I test fired, but did not group the rifle personally. The guy said it groups good though. And this was between factory drilled centers, definitely nothing to do with chucking.
 

Lowlight

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#14
The Results are the key,

I have seen a lot of smiths attack the barrels as being out of spec, etc, and then I talk to others who have great success with them, and the common theme is the way they spin them up.

The guys who don't like them, say they are out of spec, the guys who like them, and have good results with happy customers say it takes longer to chuck them up correctly. It's a bit more set up because the barrel can and will flex more than a traditional steel barrel. I see guys crow about the steel Proof barrels, but then complain about the carbon fiber ones, yet the barrels are the same. The wrap is the only real difference, the process is the same.

Now I heard they were switching to a button cut barrel, but i have been to Proof and they have Rifle cut machines already set up so I find it weird they would switch when the shop is set up like a Japanese factory and is complete. Why would they redesign and restock the shop to switch machines? seems odd to me, but I have not spoken to them.

More and more as I dance around the internet, I see people happy with the results, but at the same time, I see select gunsmiths trash them. I think part of it goes to the Precision Rifle Blog hit job on them. They had a to some crazy ass test to get them to flex in a meaningful way. That test then got published Bryan Litz. Even early on, when guys were claiming they were "walking" when getting hot, I found it to be Mirage and not the barrel. If you shoot it hard and fast you get a ton of mirage which causes issues. When I blocked the mirage the barrel was shooting true. Very few people mention this part of it.

I have traveled to both Christensen Arms and Proof to see the barrel making and Proof is definitely a better barrel and their shop is dedicated to the process. I have the videos, the images, etc, and I have been to other barrel makers like Bartlein, so being behind the scenes helps form opinions.
 

tlsmith22

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#15
My smith loves Proof barrels, he said he has only seen two like this and both were recent purchases from Stockys. He said the other one shot, it just wasnt concentric.
 

AIAW

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Now I heard they were switching to a button cut barrel, but i have been to Proof and they have Rifle cut machines already set up so I find it weird they would switch when the shop is set up like a Japanese factory and is complete.
That's the piece that I had heard. You'd be able to confirm without a doubt more so than any of us, but word is that it's just the prefits that are going this route since it is a much faster rifling process.
 

tlsmith22

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#18
The other two are on the barrel. There was little to no deflection on the dial indicator on the range rod. It is taking so long to upload pics today. I just uploaded the one on the range rod.
 

dimar1492

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#19
I think what he's getting at is that the bore starts off-center of the blank. I'm guessing what he's trying to show in the pics is that the range rod is dialed in and when you indicate the outside of the blank it runs out .008". I assume the run out most of you are referring to would be of the bore over the length of the blank. .008" off center at the beginning of the breach is quite a bit. Chambered a few like that and it was not an issue on target.
 
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Lynn Jr

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#20
I think what he's getting at is that the bore starts off-center of the blank. I'm guessing what he's trying to show in the pics is that the range rod is dialed in and when you indicate the outside of the blank it runs out .008". I assume the run out most of you are referring to would be over the length of the blank. .008" off center at the beginning of the breach is quite a bit. Chambered a few like that and it was not an issue on target.
Exactly
The Smith is pointing out something most can verify at home with cheap calipers.
Measure the thickness of the muzzle in 4 positions ~ 90 degrees apart making sure you are in a groove.
Most would think the profiling process corrects this like it did in the past but today they use blanks closer to the finished diameter.
 

Threadcutter308

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#21
I cannot speak of Carbon fiber wrapped barrels as I have no experience with them.

I believe that when a barrel manufacturer processes a steel/stainles barrel, he will first gundrill a blank (straight cylinder) to the rough bore dimensions. Then he either cut rifles or button rifles the lands/grooves in the bore. After that, he may or may not lap the barrel, but, he does go on to cut the countour of the barrel. When he cuts the contour, it is common to use a dead center on a backing plate with a dog holding the barrel in place, on the dead center/backing plate. This is done at the headstock of the lathe and the tailstock uses a live center, both ends (live center and dead centers) being inserted into the bore. After cutting the contour with a cutting bit in the lathe, the contour is also belt sanded to remove the tooling marks. It is very possible that the sanding of the exterior of the contoured blank introduces the diametrical errors that the OP's 'Smith observed. With that in mind, I believe it is more correct to say that the contour is not concentric to the bore, not the other way around.

Whenever I thread/chamber a barrel, I always dial in the bore with range rods and .0001" resolution Mitutoyo dial indicators, one on each end. I fix the barrel through the spindle/headstock. I use a 4 jaw chuck in the headstock and a 4 point spider in the outboard (left) side of the headstock/spindle. It takes time to dial in, but I can get concentricity to .0002" to .0003" TIR. I also locate the "high spot" (thickest part) of the muzzle and index it to the bottom (6 O'Clock) position when I cut the threads for the trunion. In doing so, I have isolated the incosistency to the vertical axis, where I can simply dial in more or less elevation on the finished product to compensate. The last place I want that incosistency is at the 3:00 or 9:00 O'clock position(s). If the error is in the 3:00 or 9:00 O'clock position, the more windage correction is required as the target distance increases.

I think there is a common mis-conception that the barrel blank is contoured first, then is drilled/bored. I tend to think that errors much larger than .008" would be very common if the blank was contoured first, then bored/gundrilled. If you think about it, as long as both ends of the bore were prepped such that the live/dead centers were perfectly aligned in the center of the bore (perfectly concentric), the contour could be cut such that the OD of the countoured blank would be perfectly concentric with the OD of the bore.

Personally, I don't get concerned about .002" or .003" of variation of bore to OD of contour. I just index the thick part of the muzzle to the 6:00 O'clock position. Seems to work just fine. What IS most important to me is that the Bore is Straight (unto itself). I really don't care about the bore's relationship to the contour, unless it's ridiculously out of whack.
 
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tlsmith22

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#22
I think what he's getting at is that the bore starts off-center of the blank. I'm guessing what he's trying to show in the pics is that the range rod is dialed in and when you indicate the outside of the blank it runs out .008". I assume the run out most of you are referring to would be of the bore over the length of the blank. .008" off center at the beginning of the breach is quite a bit. Chambered a few like that and it was not an issue on target.

That is correct. That’s is what he is showing me. He hasn’t checked the other end yet, or hadn’t earlier when I talked to him. He has built 1000s of guns and several for me. I trust his opinion on it. I was just curious if a lot of you guys had seen the same thing.
 

clcustom1911

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#23
My pre-fit Proof I purchased a couple months ago shoots itsy bitsy groups with multiple bullets (Norma Golden Target, Hornady 147 ELD-M, and JLK 130's) so if it's not concentric, I sure can't tell.
 

Lynn Jr

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#24
That is correct. That’s is what he is showing me. He hasn’t checked the other end yet, or hadn’t earlier when I talked to him. He has built 1000s of guns and several for me. I trust his opinion on it. I was just curious if a lot of you guys had seen the same thing.
Yeah in the old days you could order up a 1.750 straight cylinder barrel and it was cut from a 1.875 blank. Today the gun drilling is supposed to be more accurate so some shops start with a 1.750 blank.
My finished product after grinding and 320 sanding ended up at 1.660 inches and 0.060 of taper to the muzzle.
They used a straight cylinder program in the surface grinder so I got a free barber stripe running most of the barrel length.
It was not a proof barrel.
0.008 as I posted earlier is common despite contouring between centers sanding and surface grinding.
 

Rubicon Precision

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It’s of no concern. The only time I even worry about what the OD of the barrel is doing is when blending a muzzle brake/seamless thread protector, and that is after the threads were cut aligned with the bore.

In other words, it’s normal and nothing to worry about.
 

DAVETOOLEY

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#28
.0080" TIR Means it's out .0040" The thickness of a sheet of paper. No big deal as we work on the inside. I did a Boots Obermeyer barrel once that was unturned . It just like it had come from the steel mill. My customer wanted to leave it full size and install a muzzle break. It was out over .070" at the muzzle. I did all the chamber and muzzle work. Then to blend the break in I had to dial in the OD of the blank. That was on a 32" blank. Looked very odd when you took the break off.
 

parshal

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#33
I've chambered four carbon Proof barrels and two steel. All were perfectly centered when the barrel was held between centers. Two of the barrels were from Stocky's, one from Brownells and the other direct from Proof. The last carbon was direct from proof in October. The Stocky's ones were two years ago. I wonder what's changed.
 

t_brooks

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#34
This seems like a good place to ask a question about these CF barrels. Does anybody know the process Proof or Christensen uses for wrapping the barrels. I would assume drill, rifle, contour and then wrap. I've always been told to not flute a button rifled barrel by a button rifle manufacturer himself. Assuming this is true wouldn't cut rifle barrel only be the logical choice and why in the hell would a manufacturer use a button rifled barrel to wrap in CF ?
 

Bowhntr4life

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I have seen many proof barrels spun up and never an issue. It seems odd to me to have 2 in a run, but I guess it is possible. I would say it’s smith error.
 

GH41

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#36
"Assuming this is true wouldn't cut rifle barrel only be the logical choice and why in the hell would a manufacturer use a button rifled barrel to wrap in CF ? "

So you wouldn't turn a sporter weight conture on a button rifled blank either??
 

Jmcmath

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#38
This seems like a good place to ask a question about these CF barrels. Does anybody know the process Proof or Christensen uses for wrapping the barrels. I would assume drill, rifle, contour and then wrap. I've always been told to not flute a button rifled barrel by a button rifle manufacturer himself. Assuming this is true wouldn't cut rifle barrel only be the logical choice and why in the hell would a manufacturer use a button rifled barrel to wrap in CF ?
  • Proof CF barrels are contoured and then wrapped before rifling. It appears it goes drill,contour,wrap,rifle.
  • Correction* rifling before wrapping.
  • They are cut rifled
  • Even cut rifles manufacturers (Krieger) say not to flute their cut rifled barrels.
 
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Jmcmath

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#40
I will watch the video, may even call proof. My information was from this.
22796AED-A82D-454B-9E8A-4937FA62BCA6.png

Re-edit
Ok, watched the video... says they rifle before wrapping and after contour. Interesting
 
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HellsCanyonArmory

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#45
There’s a reason barrel makers ask you to specify a finish length on the Barrels your order. So they can contour it on centers close to intended finish length. They do this because no barrel bore is perfectly straight and if you were to cut the lengths down significantly you’ll almost always see the bore being off-center.

For your average builder, straight barrels shoot better because they work best with traditional gunsmith methods. I’ve had some insanely crooked barrels shoot fantastic and I’ve had string straight Barrels that shot like crap.

Mike
 

Edds

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#46
When you crown a barrel, you can make a tapered cut about an inch long on the OD of the muzzle then spin it and it will look perfect. I've seen a video of a CNC crown job on this website that showed that. I think Rubicon Precision posted the video. Maybe a Proof barrel doesn't have a long enough muzzle to do this but it wouldn't take much length to clear up .008".
 
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#48
When you crown a barrel, you can make a tapered cut about an inch long on the OD of the muzzle then spin it and it will look perfect. I've seen a video of a CNC crown job on this website that showed that. I think Rubicon Precision posted the video. Maybe a Proof barrel doesn't have a long enough muzzle to do this but it wouldn't take much length to clear up .008".
I don’t think that was my video, but I do taper out of the OD slowly when doing a crown. This is an old video, so I can’t remember the exact number, but I probably tapered out of the radius to the OD around .200”. This small muzzle didn’t have much to work with, so the radius is probably only around .02”.

When blending a brake or thread protector, I taper out even slower.

And it is certainly a dirty, unoptimized one-off program...don’t judge!

 

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