Why dial a rifle bore within .0001"

[Edd]

Then why wouldn't you dial it in that way and cut the rear of the chamber and the shoulder to run true with those two points?

 

[J E Custom]

Ive never seen the kind of straightness and TIR you describe.

Ive done two bartliens and one krieger in the last month or two and none had a bore straighntess even close to .005".

Diametrically they were all probably within .0001 from end to end and probably within .0001 of advertised size, but nowhere near straight.

If i indicate both ends the bore always jump ropes enough to easily see with the eye.

Typically i get barrels with a TIR of about .005-.010 on the ends, but ive never seen one where the bore is straight or concentric all the way through.

I typically indicate the bore as long as i can reach from the chamber end, and let the muzzle do whatever it needs to so i can get the area where the chamber reamer will be piloted, to run as true as possible.

When i do this, typically the muzzle will run out .01-.02".

Is this not the preferred method?

I have dealt with these tolerances for years and have a list of barrels that I wont use for that reason.

Some barrel manufactures build barrels and then grade them from 1 to 4 and other barrel makers make barrels to a spec and if they don't fall at or under that spec. they are rejected. And some barrel makers resort to mechanical straightening. I wont by or use any barrel that has been straightened.

Most barrels will have some run out on the outside because of the contouring process and the barrel finish and this has to be dealt with if it is over .002 . from what I can find out from most barrel makers .005 to .007 is the acceptable limit of this run out. I have several barrel makers that know not to send me a barrel with anything more than the bore spec. (.0001) and the outside run out more than .002.

Maybe I am to picky, but if they advertise a maximum tolerance, I expect them to deliver what they say.

I once had a barrel maker that had to make 3 barrels before one would match/beat there advertised spec. the other barrels were good but just not good enough to meet there #1 barrel tolerances.

After building the rifle (A 416 Buffalo) it shot the best group of my life (.034 with a 400 grain bullet).
so for me this was conformation that quality and precision of the barrel is paramount if accuracy is the goal and the rest is up to the smith.

I have heard stories of barrels that were indexed because of barrel run out, I would consider that barrel to be junk and would never use one or buy another from that maker.

I am not good enough to turn carbon into diamonds, so I demand the best I can get and wont compromise my standards. (I need all the help I can get).

J E CUSTOM

 

[Canadian Bushman]

I have dealt with these tolerances for years and have a list of barrels that I wont use for that reason.

Some barrel manufactures build barrels and then grade them from 1 to 4 and other barrel makers make barrels to a spec and if they don't fall at or under that spec. they are rejected. And some barrel makers resort to mechanical straightening. I wont by or use any barrel that has been straightened.

Most barrels will have some run out on the outside because of the contouring process and the barrel finish and this has to be dealt with if it is over .002 . from what I can find out from most barrel makers .005 to .007 is the acceptable limit of this run out. I have several barrel makers that know not to send me a barrel with anything more than the bore spec. (.0001) and the outside run out more than .002.

Maybe I am to picky, but if they advertise a maximum tolerance, I expect them to deliver what they say.

I once had a barrel maker that had to make 3 barrels before one would match/beat there advertised spec. the other barrels were good but just not good enough to meet there #1 barrel tolerances.

After building the rifle (A 416 Buffalo) it shot the best group of my life (.034 with a 400 grain bullet).
so for me this was conformation that quality and precision of the barrel is paramount if accuracy is the goal and the rest is up to the smith.

I have heard stories of barrels that were indexed because of barrel run out, I would consider that barrel to be junk and would never use one or buy another from that maker.

I am not good enough to turn carbon into diamonds, so I demand the best I can get and wont compromise my standards. (I need all the help I can get).

J E CUSTOM

I personally didnt know the extent of the tolerances at which barrel mfg. can gun drill and ream consistently, nor do i know all the makers processes and adv. tolerances.

I am certain i have never cut a barrel that was straight and true to .002 to begin with, and now that i know you have i kinda feel like ive been getting the shorter end of the stick. Perhaps a little research and a few emails may be in order.

I have and do clock barrels that have excessive run out but i really dont like doing it. Id much rather have them all run within a few thou and only cut the shoulder once.

 

[Canadian Bushman]

Then why wouldn't you dial it in that way and cut the rear of the chamber and the shoulder to run true with those two points?

You can, and some smiths do, but you are assuming that the barrels bore runs straight and true between those two points. Often with gundrills the path of the hole is a long arc or even a corkscrew. Sometimes the reaming process eliminates this ( partially ) but a reamer will typically follow the bore ( reamers styles and shapes affect thier ability to do this ).

If the chamber reamer is fighting to follow a hole because the angle of inclination is to great, it will increase cutting forces, and usually cause one side of the reamer to do more cutting than the other if not all of it and the result will be a chamber that differs from the actual shape of the reamer. It could even cause a bad finish or chatter. My biggest worry is freebore that isnt concentric to the major dia of the rifled bore.

Now i personally believe it takes much more than a few tenths to cause a piloted reamer to do this to any significant effect, and i also believe things like poorly ground reamer or mis-aligned tail stock are much more likely to cause these problems than runout.

However if i can buck the barrel so the bore where the reamer is cutting will be as straight and centered as im able to get it, then hopefully the reamer will center up and cut within a very small tolerance of where it was ground.

If i had a guy who insisted i cut his barrel in that manner i wouldnt be opposed to doing it. I think most barrels run good enough the reamer would follow and also the barrel would center in the stocks channel perfectly with no timing. I know some guys who used to cut barrels that way and all of them say that most of the barrels shot well and some shot really well.

On a side note, a gunsmith that i know and use, and believe to be a very talented machinist once told me a customer brought him a barrel that ran out very bad. Smooth well sized bore but "hooped" big time in the middle. He called the customer, showed him the barrel running in the machine, and the customer told him to cut it. So he did. Customer reported it was one of the better shooting barrels he owned. Ill buy you a beer and lunch if you can explain that one.

 

[Edd]

You can, and some smiths do, but you are assuming that the barrels bore runs straight and true between those two points.

Actually, I am assuming the barrel does not run true between those two points. If you can get an inch of the bore on both ends to run within .0001-.0002" true and bore the rear of the chamber behind one of those points, wouldn't the reamer pilot only run on that inch that was dialed in. You would have the chamber, the shoulder, the point where the bullet enters the barrel, and the point where it exits the barrel all running true. There isn't anything you can do about the 20 or so inches in between those two points.

 

[Canadian Bushman]

Actually, I am assuming the barrel does not run true between those two points. If you can get an inch of the bore on both ends to run within .0001-.0002" true and bore the rear of the chamber behind one of those points, wouldn't the reamer pilot only run on that inch that was dialed in. You would have the chamber, the shoulder, the point where the bullet enters the barrel, and the point where it exits the barrel all running true. There isn't anything you can do about the 20 or so inches in between those two points.

I misunderstood. I thought you literally meant the "ends" of the barrel.

Most reamers pilot about 2-3" in from the chamber end, but nonetheless this could be achieved all the same.

If you brought me a barrel and wanted it cut that way, i would do it. I dont pretend to know exactly what makes a barrel shoot. If its your barrel and your money you should get what you want.

 

[Pdvdh]

Here's the methods of chambering and fitting a barrel Hired Gun describes on his website. Which leaves me wondering how J E Custom is rounding up barrel blanks with such little deviation from perfectly straight, chamber to muzzle?
Pricing

"Once passing quality control inspection your barrel is carefully mounted in the lathe. We dial in the barrel only on the end we are working on. When it's the chamber we dial two locations. The first one is right where the throat is to be located and then two inches farther in. All rifle barrels have a slight curve in the bore. The technology to drill a perfectly straight bore 30" deep is still too cost prohibitive for rifle barrels. Our goal is to get the chamber and throat perfectly aligned with the path of the bore. We use Starrett .0001" indicators with long reach styluses or Grizzly rods to reach up to 6" into the bore. We do not settle for .0002" variance as most shops do. We go the extra mile and keep dialing until the .0001" indicator is running dead zero. No detectable movement. Why go to this trouble? We do it because it is one of the many variables in a rifle we can control and eliminate.

Once dialed, the first thing is the position of the curve in the bore is notated and when the action threads are cut the curve of the bore is timed to torque up in the 12 o'clock position. If the curve is outside our limits the barrel is rejected. I can't reject any curve in the bore or we would be rejecting them all. We prefer to see this run out be no more than .020". Bartlein and Krieger are sometimes running less than .005" run out.

The threads are precision fit to your action and allow the tightest fit possible to your action. This precision fit is critical for the barrel action joint to behave as one under the pressures of firing. No CNC can match the fit we can achieve to your action.

Now the flush system is fired up to flush all machine swarf away from the cutting edges and out of the barrel during the internal machining operations. The chamber is roughed out to a depth equal to the shoulder of the cartridge and about .015"- .020" undersize. Then go in with an indexable tooled boring bar equipped with a carbide cutter. We then bring it to within .005"-.010" of final diameter. Then the precision chamber reamer is brought in and the chamber is cut to final size. Headspace is set with gauges from zero to plus .002" depending on the application and customer preference.

Once the chamber end is done the barrel is removed from the lathe and turned around to cut the crown and muzzle brake threads if so equipped. We use the same care to dial in the barrel for the crown and muzzle brake as we do the chamber. We dial in where the crown is to be and 2" back. We want that crown perfectly perpendicular to the actual bore. We cut super sharp 11 degree crowns."

 

[Canadian Bushman]

Thats pretty much the process i use.

Notice how specific he is about which part of the bore and the length which he indicates to .0001.

 

[J E Custom]

I personally didnt know the extent of the tolerances at which barrel mfg. can gun drill and ream consistently, nor do i know all the makers processes and adv. tolerances.

I am certain i have never cut a barrel that was straight and true to .002 to begin with, and now that i know you have i kinda feel like ive been getting the shorter end of the stick. Perhaps a little research and a few emails may be in order.

I have and do clock barrels that have excessive run out but i really dont like doing it. Id much rather have them all run within a few thou and only cut the shoulder once.

I not only feel lucky, I feel good that I get that quality. I am sorry that you haven't been and your
idea to research is a good one and may be an eye opener.

I have changed barrels over the years because of quality and not having to worry about cost has
prompted me to use only barrels that met the advertised tolerances. And actually the better quality has lowered set up time (Time is money) and made it easier to produce good quality.

My rule is simple, look for a barrel that meets the tolerance I expect, then expect to get that quality
because I am paying for that quality. I am not interested in A barrel maker that doesn't post his acceptance criteria, so I only buy from the ones that do and only as long as they honor there guarantee of quality and tolerances.

Maybe using all quality parts has kept me out of trouble, And I'm not as good as I would want to be.

I personally like to indicate both ends at the same time to find straightness. There may be a better way but if I can get both ends to indicate .0001 or less at the same time I feel it is straight. if both ends wont indicate with each other, then its just a matter of doing the math and figuring out just how crooked the bore is for its entire length.

Anyway, there are barrels that are made straight you just have to look for them and except no less.

J E CUSTOM

 

[IdahoCTD]

I personally like to indicate both ends at the same time to find straightness. There may be a better way but if I can get both ends to indicate .0001 or less at the same time I feel it is straight. if both ends wont indicate with each other, then its just a matter of doing the math and figuring out just how crooked the bore is for its entire length.

Anyway, there are barrels that are made straight you just have to look for them and except no less.

J E CUSTOM

Have you tried indicating in the barrel 2+" when both ends are running true? You might be surprised how not straight it is. They are suppose to be turned on centers so the ends are usually good but the middle can be a jump rope. I cut one barrel from a 27" blank to a 22" finish and the bore was out of center .030" in 5". I dialed in the chamber end in and the bore had .156" of total travel or .078" of run out. It still shot good but that tells you how not straight some barrels are.

 

[J E Custom]

Have you tried indicating in the barrel 2+" when both ends are running true? You might be surprised how not straight it is. They are suppose to be turned on centers so the ends are usually good but the middle can be a jump rope. I cut one barrel from a 27" blank to a 22" finish and the bore was out of center .030" in 5". I dialed in the chamber end in and the bore had .156" of total travel or .078" of run out. It still shot good but that tells you how not straight some barrels are.

The deeper/longer the tool goes into the bore the more accurate the reading. PT&G makes a precision ground gauge that goes in until it stops, indicating that the bore is not straight but I have not used one of there gauges because they will only tell you that the bore is not straight, Not by how much.

This jump rope effect is normally because the contour was cut improperly and tool push caused the barrel to deflect. As I mentioned earlier, some barrel makers mechanically straighten barrels after they are bored, rifled and contoured to make the bore straight. when done this way the od of the barrel is not true to the bore making the barrel wall uneven in thickness. (I don't use these barrels unless I re-contour the od of the barrel to true it up with the bore.

It is simple, in order to get a good barrel the OD has to be true to the bore and the bore has to be straight. If this is not the case, you have a pig in a poke (Unpredictable).

I knew there were bad barrels out there but not as many as this post suggest. this will stop if everyone will just send the barrel back. We (Long range shooters) are greatly responsible for the quality of the newer bullets because we complained and the bullet manufactures had to respond or shut there doors, Barrel makers need to be held to higher standards if they want to stay in business

I check every barrel (Even my favorite brand)to verify the quality before I start to prevent letting a poor quality barrel from finding it's way in a precision rifle. In my opinion,anyone that has the skill to find a bad barrel should reject it and demand better from their barrel maker. This is also the reason I wont use a pre chambered barrel. it is to late to worry about tolerances and quality. I don't want to find out later after all the machining is done that the poor shooting rifle was caused by a bad/poor barrel.

J E CUSTOM

 

[IdahoCTD]

I guess the point is......very few barrels are under .005" of runout when you dial in the chamber end with a long reach indicator or a grizzly rod. It is hard for a company to drill a 27+" long hole perfectly straight. There are way too many thing that can and will prevent it from going perfectly straight. Several companies are using hones on the bores prior to rifling and it seems to help a bit. Just because the bore isn't perfectly straight doesn't mean it won't shoot good. Most barrels shoot really good even with .020-.030" of run out.

 

[Canadian Bushman]

Krieger just emailed me back and said their goal is .01 TIR across a 27" blank and .001 on the ends. They do not guarantee this and expect it to increase with longer blanks.

Awaiting responses from other makers.

 

[IdahoCTD]

I use a lot of Bartlein's and they have been really good on average but the best was still .0025". I've had a few around .025" but most are under .010". I haven't done a Krieger in a while so we'll see how it goes when I do my 7-338 Norma Imp with a Krieger in the next little bit. Benchmarks run closer to .020-.025" on average. I did a Proof barrel that was over .050" not too long ago and still shot good. I did a X-caliber barrel that was .0055". I was pretty impressed with that.