Barrel harmonics question

[Welderboy11972]

Hey guys, I've got a question for some of the experienced smith's on here. I've been watching videos on youtube about trueing actions and barrel installs. On a couple of the videos, they showed why it's important to index the barrel from the bore not the outside of the barrel, when cutting treads and reaming the chamber. This makes perfect sense to me. But, none of them in the video went on to say anything about how the difference in the runout, of the bore vs the outside of the barrel, effects the harmonics of the barrel.

If the barrel metal is thicker, from bore to outside barrel Dia, on one side thicker then it is on the other, wouldn't it effect the harmonics of the barrel?

Do any of you machine the outside of the barrel in this situation?...after indexing off of the bore.

Is this something that isn't worth worring about?

 

[J E Custom]

Hey guys, I've got a question for some of the experienced smith's on here. I've been watching videos on youtube about trueing actions and barrel installs. On a couple of the videos, they showed why it's important to index the barrel from the bore not the outside of the barrel, when cutting treads and reaming the chamber. This makes perfect sense to me. But, none of them in the video went on to say anything about how the difference in the runout, of the bore vs the outside of the barrel, effects the harmonics of the barrel.

If the barrel metal is thicker, from bore to outside barrel Dia, on one side thicker then it is on the other, wouldn't it effect the harmonics of the barrel?

Do any of you machine the outside of the barrel in this situation?...after indexing off of the bore.

Is this something that isn't worth worring about?

There are many ways to solve this problem. I personally spin every barrel between centers and measure the run out, If it exceeds 3 or 4 thousandths I ether reject it and send it back to the barrel maker, Or I re-contour it to true it up.

This run out, if left alone can cause a shift in POI as it heats up. the Harmonics will normally remain the same, until you re-contour and then it will change.

Some say that .005 to .007 thousandths is ok, Not knowing where the limit is I hold it to no more than .003 thousandths TIR. If the barrel has NO run out I feel I have the best chance of a real shooter because of consistent wall thicknesses.

Just My limits. (I don't like working around a problem, I prefer to eliminate it).

J E CUSTOM

 

[Welderboy11972]

Thanks...that is what I was thinking. I just wanted to make sure I was on the right page.

I wasn't knocking the smiths in the videos. It's possible that they were using a bad barrel just to give a better demonstration of the process. I was more wondering what the right thing to do in this situation. Thanks again.

 

[shortgrass]

From one end of the barrel to the other, that is not a perfectly straight hole to begin with.

 

[tbrice23]

From one end of the barrel to the other, that is not a perfectly straight hole to begin with.

Could this explain why no (or few) barrels will have the exact same load preference even if they are on an identical acton, stock and scope and from the same manufacturer heat # and reamer ??

 

[shortgrass]

Could this explain why no (or few) barrels will have the exact same load preference even if they are on an identical acton, stock and scope and from the same manufacturer heat # and reamer ??

Because no two (or three, or more) things on this earth are "identical",,,, meaning exactly alike.

 

[Greyfox]

Several years ago our rifle club got a full tour of the Savage plant. They were an hour from our club and attended and sponsored a lot of our LR events so we developed a great relationship with them. This was when the then CEO(Ron Coburn) had decided to re-define Savage rifles for long range precision shooting. While on tour they us through each of the stages of the production process. Interestingly, every barrel was tested not only for concentricity, but also checked for straightness. Straightening was performed by an individual that would look through the barrel at a light and if off center(bent), would put the barrel in a very large tube bender and straighten the barrel. As we were all quite surprised given the highly sophisticated CAD, and other state of the art production machinery used through most of the production process that such an unsophisticated approach would be used to straighten the barrel. The operator had this job for decades and could achieve straightness within a couple of thousandths of an inch! Fascinating to watch. Overall, we were impressed at the attention to detail, particularly when it came to barrel production. They overly stressed the importance of precision concentricity, straightness, and rifling and demonstrated the processes and tests used to achieve this. It certainly explained the reputation they were quickly earning for producing one of the most accurate factory rifles. We eventually had to reclass our competition categories because the Savage target grade factory rifles were performing at custom class levels.

 

[Canadian Bushman]

From one end of the barrel to the other, that is not a perfectly straight hole to begin with.

+1

This sums up my experience with gun drilled holes.

 

[J E Custom]

+1

This sums up my experience with gun drilled holes.

Barrel straightening use to be the norm and all barrel makers had the equipment to do so. with the newer/better drilling machines it has become less mandatory and more optional.

Some custom barrel makers have perfected there drilling and reaming to the point that barrel straightening can be ruled out and only an occasional barrel will be rejected due to run out. some of these rejected barrels can be drilled to a larger diameter and reamed and rifled to within tight tolerances. (Expectable within there advertised criteria).

Most premium barrels are within .002 to ,005 thousandths straightness and many are so close that they cannot be measured with most of the available (affordable) Indicators.

But, even with perfect/identical barrels and done buy the same smith and with the same reamer, It would be very rare to have the same load and performance in two different rifles with the same cartridge.

J E CUSTOM

 

[Canadian Bushman]

Barrel straightening use to be the norm and all barrel makers had the equipment to do so. with the newer/better drilling machines it has become less mandatory and more optional.

Some custom barrel makers have perfected there drilling and reaming to the point that barrel straightening can be ruled out and only an occasional barrel will be rejected due to run out. some of these rejected barrels can be drilled to a larger diameter and reamed and rifled to within tight tolerances. (Expectable within there advertised criteria).

Most premium barrels are within .002 to ,005 thousandths straightness and many are so close that they cannot be measured with most of the available (affordable) Indicators.

But, even with perfect/identical barrels and done buy the same smith and with the same reamer, It would be very rare to have the same load and performance in two different rifles with the same cartridge.

J E CUSTOM

If you are getting barrels within .002-.005" straightness, that is amazing.

How are you measuring the straightnes of a 30" hole?

 

[shortgrass]

You can set a barrel up, between centers, and measure run-out in a dozen places. You'd be measuring what lies between the centers on the outside. But, the tool that does the drilling, the gun drill, 'wanders' ever so slightly in its' journey from beginning of the hole to the end of the hole. It's the 'nature' of drilling any hole, whether it be a hole 28" long or one 2.8" long. The 'wandering' is induced by rotation, the imperfections of the material being drilled and the imperfections of the cutting tool, itself. I believe we're only talking a few tenths of a thousandth here. It could be more, but who has the capability to measure it? NOTHING in this world is perfect. The bore reamer that follows the drilling takes some of that 'wandering' out, but not all of it. Which means, in some places along the length of the barrel, the wall of the bore is closer to the O.D. than it is at other places. In reality, it is a non-issue for todays premium barrel makers as the barrels they make are just that,,,, premium,,,,,,, and they'll out shoot 99.999% of their owners.

 

[Canadian Bushman]

You can set a barrel up, between centers, and measure run-out in a dozen places. You'd be measuring what lies between the centers on the outside. But, the tool that does the drilling, the gun drill, 'wanders' ever so slightly in its' journey from beginning of the hole to the end of the hole. It's the 'nature' of drilling any hole, whether it be a hole 28" long or one 2.8" long. The 'wandering' is induced by rotation, the imperfections of the material being drilled and the imperfections of the cutting tool, itself. I believe we're only talking a few tenths of a thousandth here. It could be more, but who has the capability to measure it? NOTHING in this world is perfect. The bore reamer that follows the drilling takes some of that 'wandering' out, but not all of it. Which means, in some places along the length of the barrel, the wall of the bore is closer to the O.D. than it is at other places. In reality, it is a non-issue for todays premium barrel makers as the barrels they make are just that,,,, premium,,,,,,, and they'll out shoot 99.999% of their owners.

Yes exactly.

Ive seen gun drills drill very very nice holes, and ive seen them drill very crooked holes. A bad grind or an operator in a hurry can make a gun drill do some wacky stuff.

Ive literally indicated and trued hundreds of gundrilled parts before i ever touched a rifle barrel or a grizzly rod.

If you can look down a barrel and see it needs to be straightened, you are a mile away from a couple thou out.

As a machine shop we have gotten away from gundrilling certain materials and now hole pop them, just because how crooked the holes were coming out.

 

[J E Custom]

You can set a barrel up, between centers, and measure run-out in a dozen places. You'd be measuring what lies between the centers on the outside. But, the tool that does the drilling, the gun drill, 'wanders' ever so slightly in its' journey from beginning of the hole to the end of the hole. It's the 'nature' of drilling any hole, whether it be a hole 28" long or one 2.8" long. The 'wandering' is induced by rotation, the imperfections of the material being drilled and the imperfections of the cutting tool, itself. I believe we're only talking a few tenths of a thousandth here. It could be more, but who has the capability to measure it? NOTHING in this world is perfect. The bore reamer that follows the drilling takes some of that 'wandering' out, but not all of it. Which means, in some places along the length of the barrel, the wall of the bore is closer to the O.D. than it is at other places. In reality, it is a non-issue for todays premium barrel makers as the barrels they make are just that,,,, premium,,,,,,, and they'll out shoot 99.999% of their owners.

+1

In an attempt to get the best performance from a barrel there are several ways that I have found that will get you very close in finding the straightness of the bore. The outside of the barrel is another issue and can be dealt with only if the bore is straight.

I use several methods to at least prove that the bore is within reason. I prefer that the barrel has no more than .0003 range in diameter for the land diameter for the entire length of the barrel. Barrel straightness should be no more than .001 for entire length but I have found that .002 will still out shoot most shooters/hunters. The out of round from center to center of the contour (Outside) anymore than .002 will be re contoured to true it up, If done correctly the run out can be immeasurable with indicators that read in .0001 thousandths.

For checking bore straightness, I use a bore straightness gauge that has a tolerance of .0001 (There is one that the tolerance is .00005 but it is difficult to use because of the allowable land diameter consistency of .0001) It is inserted into the bore with the proper bushings and eased down the bore. If it stops, It is out of straightness by over .0001 over 6" x barrel length. I then go to the bore straightness gauge with .001 tolerance and if it doesn't pass through the bore end to end the barrel has more than .005 thousandths out of straightness in 30 "end to end. and I have to use 12" range rods in both ends of the barrel to calculate the total straightness measuring run out at both ends for every 12". Both systems combined will get you very close to the actual straightness of a barrel and depending on use the decision to use it will be easier.

It is not perfect but as Short grass said "nothing is", but it gets me close. and so far, if the barrel land diameter and the straightness is at or below "My limit" and I true up the outside of the barrel to the bore by re- contouring. The rifles will normally out shoot most people. I don't claim to know what actual out of straightness is maximum that should be trashed/rejected but I do know that straight and consistent is best.

There are lots of other things that should be held to minimum tolerances to allow the barrel to do its part in making an accurate rifle.

Nothing worthwhile is easy.

J E CUSTOM

 

[Canadian Bushman]

+1

In an attempt to get the best performance from a barrel there are several ways that I have found that will get you very close in finding the straightness of the bore. The outside of the barrel is another issue and can be dealt with only if the bore is straight.

I use several methods to at least prove that the bore is within reason. I prefer that the barrel has no more than .0003 range in diameter for the land diameter for the entire length of the barrel. Barrel straightness should be no more than .001 for entire length but I have found that .002 will still out shoot most shooters/hunters. The out of round from center to center of the contour (Outside) anymore than .002 will be re contoured to true it up, If done correctly the run out can be immeasurable with indicators that read in .0001 thousandths.

For checking bore straightness, I use a bore straightness gauge that has a tolerance of .0001 (There is one that the tolerance is .00005 but it is difficult to use because of the allowable land diameter consistency of .0001) It is inserted into the bore with the proper bushings and eased down the bore. If it stops, It is out of straightness by over .0001 over 6" x barrel length. I then go to the bore straightness gauge with .001 tolerance and if it doesn't pass through the bore end to end the barrel has more than .005 thousandths out of straightness in 30 "end to end. and I have to use 12" range rods in both ends of the barrel to calculate the total straightness measuring run out at both ends for every 12". Both systems combined will get you very close to the actual straightness of a barrel and depending on use the decision to use it will be easier.

It is not perfect but as Short grass said "nothing is", but it gets me close. and so far, if the barrel land diameter and the straightness is at or below "My limit" and I true up the outside of the barrel to the bore by re- contouring. The rifles will normally out shoot most people. I don't claim to know what actual out of straightness is maximum that should be trashed/rejected but I do know that straight and consistent is best.

There are lots of other things that should be held to minimum tolerances to allow the barrel to do its part in making an accurate rifle.

Nothing worthwhile is easy.

J E CUSTOM

When you decide a barrel isnt straight enough, the mfg takes it back?

Out of the dozen or so barrel makers, i talked to last time we discussed this, no one told me they guaranteed any sort of straightness, and most wouldnt even talk to me about the average straightness they expect.

Krieger and brux were the only two that discussed it with me over the phone. They both said they dont guarantee any sort of straightness but they try to be inside a couple of thou.