Warning !!!!

[J E Custom]

Just a heads up for the smiths and the ones wanting to become one or already doing some barrel work.

Barrel straightness has always been an issue but lately it has become more of an issue and should be looked at by all.

I will not get into brands other than do not take this for granted just because your favorite brands may have this problem.

If you are interested read on if not sorry I can't help.

The first thing to do is place the new barrel between centers on your lathe and rotate slowly with a dial indicator in at least 5 or more positions up and down the barrel and look for runout. there are two scenarios that are possible.

First the outside is not straight. (In my opinion it should be no more than .001 or .002 TIR.
having talked to many barrel makers they have a range of .000 to .007 TIR I find that my favorite 3 or 4 barrel makers hold this to a max of .002 TIR. I have found (And rejected premium barrel
brands with up to .055 thousandths TIR). I also have one barrel maker that has a zero rejection rate and 2 more with only one rejection. (I still check every barrel, even the one with zero rejections out of over 50+ barrels to make sure I have what I paid for.

Out of straightness can be on the outside and the bore can/may be straight. If this is the case, the outside can be re contoured to match the straightness of the bore. Checking the bore straightness
is difficult for most because of instrumentation needs. Some of the experienced smiths using north light(It is the truest light) can look through the bore and see the straightness or lack of it. Other sources of light will not work.

Obviously, if a barrel is not straight on the inside or the outside it will not perform as well as if it were straight and true. so If you place the new barrel between centers it should give you an indication of the quality control of the barrel maker, and you can make an educated decision as to your decision to use it or send it back for a straight one.

I find that the cheaper brands have a much higher rejection and at some point I simply won't use there barrels because of the high percentages of returned barrels. Occasionally a bad barrel can fall through the cracks even with the best barrel makers and that is the reason for this post. I am simply saying don't get comfortable with "ANY" barrel maker if you are looking for ultimate accuracy. Checking this saved a friends reputation because he checked the TIR and found .027 on one barrel and .007 on another, both were well known brands and both has unstraight bores.

There have been all kinds of fixes posted over the years and some of them work (Like re contouring if the OD is not straight) but many don't address the real problem of an expensave
premium barrel that is not straight. I can honestly say that I don't know where the straightness limit is for accuracy degradation is, but i am uncomfortable with any more than 1 or 2 thousandths
and reject them. And feel good about a barrel with "No" runout.

Just information for those that are interested.

J E CUSTOM

 

[Edd]

Do you offer a service to check barrels for straightness?

 

[IdahoCTD]

That only tells you how close the OD of the barrel is when turned on the centers at those 2 points. IMO every manufacture should try to stay under .002 there and it shouldn't be hard for them. Bore straightness in the blank is equally important IMO. If it's way off half way through the blank it's the same as the OD being off when checking between centers. You get thin sides and thick sides to the barrel that can cause uneven movement and inconsistency. I cut a 26" Green Mountain blank down to 20" one time and the bore was out .023" from center and within .001 at the end before cutting. Makes you wonder how far out it would be at the middle of the blank. I've also seen 2 Lilja barrels that had the bores off so far from the outside it looked like a cam shaft. Not sure how those were turned on centers.

 

[tbrice23]

Is the high TIR rate due to the nature of deep hole boring? How do these manufactures miss this if they claim to be air gauging within .002" or whatever ?

 

[J E Custom]

Do you offer a service to check barrels for straightness?

Sorry Edd,
I have enough trouble with the barrels I work On but if everyone is aware of the problem they can have their smith check it.

Idaho,
If the barrel was checked before it was cut to 20" and was centered, and then cut to 20" and off center by .023 thousandths the bore was not straight in the beginning.
This is a case of the bore not being drilled straight and the outside being contoured between centers. If the bore is not straight, contouring will not help. It is not uncommon for the drill to drill a straight hole that enters the blank centered and exits the blank off center. This is why they are contoured between centers, to uniform the barrel wall to the bore.

Tbrice,
Deep hole drilling is not a perfect science and is sometimes curved from one end to the other. The drilled hole is then reamed to the size needed for the caliber and before rifling if this doesn't straighten the bore within specifications it should be rejected. (This is not always the case though). The rifling process will not straighten the bore and that Is the reason they remain crooked. Air gauging only checks the bore diameter and consistency as it is ran through the bore. Tool push is one of the causes of runout on the OD especially on thinner barrels when a following rest is not used to oppose the cutting tool to support the barrel. It was common for factory barrel bores to be straightened after contouring making the OD of the barrel have whatever runout the bore had, This condition led to poor grouping because the effects of heat of follow up shots. premium barrels "Should not" have this problem considering their cost and quality control.

Most barrel makers have high tec. lasers or other instruments that can test the straightness that most of us can't afford. So we rely on more simple methods that can only give us an idea of what we have.
there is a tool that is precision ground caliber specific that is 8+inches and very hard/ridged as not to flex very much that can be started in the barrel (Carefully) and if it goes all the way through at least you know that if it is not perfectly straight it is close. if the gauge rod only goes a few inches then you can Assume that the curve is that amount for the entire barrel. it is not perfect but at least it will give you an idea of what you have. I know that some on this site have used this method and would hope they would contribute what they know.

J E CUSTOM

 

[IdahoCTD]

It's a case of drill drift when it was drilled. Most bores are off in a cork screw pattern to some degree.

The point I was trying to make is..... checking a barrel between centers for TIR only tells you what is happening at those two points. It doesn't tell you what the bore is doing. Cutting it off 2" might lead to drastically different TIR numbers.

 

[Mike 338]

I wonder how many gunsmiths even check?

 

[oldfortyfiveauto]

Is the high TIR rate due to the nature of deep hole boring? How do these manufactures miss this if they claim to be air gauging within .002" or whatever ?

Air gaging will not find that. Normally only qualifies the bore diameter.

 

[J E Custom]

[QUOTE="IdahoCTD,

The point I was trying to make is..... checking a barrel between centers for TIR only tells you what is happening at those two points. It doesn't tell you what the bore is doing. Cutting it off 2" might lead to drastically different TIR numbers.[/QUOTE]


You are right, But the two points are the contact area of the bore and
the centers and everything else will be based off these two points. (The beginning and the end of the bore) If the barrel or bore is not straight there will be run out between these two points.

Once I establish that the OD of the barrel is straight, then I can determine if the bore is also straight to a point. we all know that drills
don't always drill a perfect hole, and that's why the bore is reamed next. reamers are designed cut straight and will true up the bore if it is not to bad.

I don't claim that it is an exact science, Checking at least gives me an idea of the quality of the barrel and if I should use it or not. All that I can prove is that It is not straight with the tools I have.

Just a heads up on a recurring problem.

J E CUSTOM

 

[stbbo]

If this is Jerry Easley from Brazoria County, Texas this man knows EXACTLY what he is talking about. His brakes are 2nd to none and he is a stand up guy. Would not hesitate having him do any work.

 

[Pdvdh]

Just a heads up for the smiths and the ones wanting to become one or already doing some barrel work.

Barrel straightness has always been an issue but lately it has become more of an issue and should be looked at by all.

I will not get into brands other than do not take this for granted just because your favorite brands may have this problem.

J E CUSTOM

The value of the Thread will increase exponentially if the barrel manufacturers were ranked in groups from better to poorer on barrel straightness.

Is the risk that the barrel manufacturers will no longer interact fairly with the gunsmiths who report on barrel straightness?

What better way to encourage barrel manufacturers to up their game performance?

 

[J E Custom]

The value of the Thread will increase exponentially if the barrel manufacturers were ranked in groups from better to poorer on barrel straightness.

Is the risk that the barrel manufacturers will no longer interact fairly with the gunsmiths who report on barrel straightness?

What better way to encourage barrel manufacturers to up their game performance?

I agree with a ranking system except for the fact that my experiences may/will be different than others and i would not want to chastise a barrel maker just because I found a percentage of barrels that were not straight. (Others may have had very good luck with the same maker if they checked them. If they haven't, then there would be no way to compare the rejection rate.

There are so many bad barrels out of 100 and depending on who got them it could be a very one sided ranking. That's why I recommend checking "EVERY" barrel no matter who made it.

These days we cannot take quality for granted with anything, so a good inspection is always beneficial in my opinion.

I am glad that this post has gotten some questions because it shows me that some do care. I have made it known that I am anal about precision and I admit it but it has served me well over the years and save my *** more than once.

J E CUSTOM

 

[Trickymissfit]

when gun drilling (the correct term for deep hole drilling) you will not get the kind of drift you see from a conventional twist drill, but you can get drift created normally by the setup or the wear in the gun drilling machine itself. The drill itself is designed to resist this, but also will do some oddball things. When the drill does stupid things, the first place you look at is the chip column. What do they look like? Even the color. A bad chip stream will send a drill all over the place due to chips binding with the cutting end of the drill. The wear on the cutting edge is another issue. If one side wears more than the other it will follow the sharper side most of the time. The coolant used is somewhat secretive, and kept as a trade secret. The pressures you work at vary with the metal. For the most part the higher the pressure the more stable the drill is. If the bushing is leaking a lot the drill will move to the side that has the lowest pressure. The operator must keep an eye on that bushing as it guides everything in the process. The guide bushing is pressurized in a hydraulic sense (the coolant system is usually split in two systems with one at an extremely high pressure and the other feeds thru the holes in the drill to blow the chips out of the hole). If the coolant gets dirty, one can expect more than just a bad finish. Most coolant systems are multi staged high volume and high pressure affairs. The filtration systems are multi staged if done right. They must be serviced daily, and often every eight hours of usage. Bypass this, and you make junk!

Another reason gun drills drill off center is with the actual machine tool alignment. Few people have a $50K laser or better yet electronic level to get this done right. These alignments need to be inspected three or four times a year. We set most of our gun drills on an isolation pad that was 24" thick. Then placed six inch angle iron all around it to prevent bumping the machine frame as well as contain the constant leakage of coolant. Holes are often reamed after drilling to get a round hole. Usually cut about .0035" all the way around. This Will Not straiten a bad hole! Just make a precise round hole that is of an accurate dimension.

I've used them from Albion to Pratt Whitneys, and the all pretty work the same way.
gary

 

[J E Custom]

Very good post and description Gary !!!!

I have watched the process but never operated a gun drill.

I also believe that the set up and the operator has a major bearing on the quality of the drilling.

Your comment about watching the chips is also correct and applies to all metal cutting.

Thanks

J E CUSTOM