secrets of straightening a barrel

Discussion in 'Gunsmithing' started by 21buck, May 24, 2011.

  1. 21buck

    21buck Well-Known Member

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    Several years ago there was an article by a gunsmith who described how to straighten out a barrel at home. I wanted to save it but time has its way and now it is gone when I really need to apply the principles to anew barrel. It seems that most barrels have somewhat of a curve in them due to in advertant heat abberations during contouring. Your help is appreciated. 21 buck
     
  2. J E Custom

    J E Custom Well-Known Member

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    Most barrels makers will tell you that .004 to .005 Thousandths Total indicated run out is
    exceptable. most smiths that have accuracy guarantees will tell you less.

    I am no expert on what is the max run out so I reject anything over .0015.

    I use barrels from makers that are normally close to 0 run out and have very good success
    with them.

    One such barrel maker explained to me that there is no real reason not to have a straight barrel
    and I could send any one that is not back and he would replace it and pay shipping.

    I have visited barrel shops and the main reason is that a barrel is contoured taking to much
    of a cut at one time and/or stress relieving was not done correctly.

    Barrels used to be straightened because the drilling process was not as good as it is now.

    Some factory barrels are still straightened but it takes a high degree of skill and special
    tools, Plus true north light.

    If you have a barrel that is not straight SEND IT BACK.

    With all of the barrels makers out there there is no reason to except anything but a good barrel
    at the cost of a premium custom barrel.

    J E CUSTOM
     

  3. Trickymissfit

    Trickymissfit Well-Known Member

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    most barrel makers are still using Pratt-Whitney gun drills from the 1950's. There are a few others out there, but most folks refuse to change, and for the most part are not anybetter. I'm not sure what they used in WWII for tooling, but I'm certain that many used the P&W's. The big difference between then and now is in the tooling, and cutting fluids (note I consider the bushing box and coolant system as tooling with these things). Drill grinds are very secretive, and often are reground off of brand new drills. How they are doing their reaming processes I can say, but it looks to me like they might be infringing on the Mapol Reamer copyrights (an extremely accurate reamer, but also very costly). The coolant is also closely guarded, and often custom mixed. The system will usually be multi filtered with at least one redundent filter system standing by. They are always at least 75 gallons and some are as big as 350 gallons. They run in a similar fashion as the basic hydraulic systems do with the same type of pumps. The grind and the bushing box are major players in keeping the bores strait and on size, and they are hydraulicly loaded with coolant and very high pressures.

    Right now Eldorado is the new kid on the block (actually since the very late 1970's), but the technology is the same. They are extremely accurate, and make gun drill that drill from both ends at the sametime. Only to meet in the middle.

    If tooled up right the blank should come out very strait (less than .0075"). But that becomes another problem as the steel lets go of it's stress as you drill; causing warpage as the drill goes thru. I looked at some photos awhile back of a barrel straitening machine in the Savage shop. Interesting, but I asked myself why? They now make machines that you can put the barrel in it, and it will do the job within .0005" in less than a minute! With very little stress involved I might add. Of course the big guys say you should never straiten a barrel after it's finished out. These guys always amaze me at how well they can cut a bore
    gary
     
  4. rscott5028

    rscott5028 Well-Known Member

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    I generally don't like cutting, bending, etc if I can't accurately and repeatably measure before and after.

    Assuming I knew enough and had the tools to do the straightening piece at home, I'm not sure how I'd measure the straightness of the bore from end to end?

    Gary/Jim - How do you measure the straightness of your bore?

    thanks!
    Richard
     
  5. J E Custom

    J E Custom Well-Known Member

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    Good advice !!!!

    I will try to explain the method used to straiten barrels.

    Before Lasers, the excepted method was to have a Master Gunsmith place the barrel In a
    special barrel press aimed at True north and looking through the bore they would apply more
    and more pressure with a hand wheel about 2 feet in diameter with the barrel held between
    two supports.

    The hand wheel was graduated so he could apply more and more bending pressure to the
    barrel and releasing it to measure rebound. the trick was not to over bend it while looking
    through the bore and moving it up and down the length of the barrel.

    This process was a highly skilled method and was very efective in its day.

    Now barrels are checked for straightness using optical methods (Lasers ETC) and mostly
    for quality control and rejected if the straightness is out of spec.

    I once had a barrel that had fell over and been ran over that was slightly bent to be re
    barreled. On the outside It was impossible to see the bend because it was so slight. but
    when held up to the north while looking through the bore you could see that it was bent.

    And about where , But With out the equipment it would be almost impossible to straighten.

    Very few custom barrel makers If any straighten barrels because of better drilling processes
    and the cost of straighting barrels in more than the barrel blank.

    I don't know what percentage of factories are still straightening barrels any more, but with there
    quality and numbers made it's no wonder that they are generally bad with an occasional
    good one.

    Straighting without specialized equipment would be hit and miss and it is easier to replace
    a barrel that is not straight than to fool with it and risk poor accuracy.

    When "Properly" placed between centers they can be measured very accurately and dealt with.

    My preferred barrel maker has a tract record of nothing but straight barrels(.0000 to .0015)
    and a rare one that might be .0025) end to end.

    The issue on how much straightness is nessary (Some barrel makers say that .007 to .010
    is OK), but as allways straight is allways better.

    I have tested factory barrels that had over .050 total run out that would not shoot at all, so
    they do exist.

    I hope this explained the process.

    J E CUSTOM
     
  6. Trickymissfit

    Trickymissfit Well-Known Member

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    if your talking a gun barrel of any real length it's a pain in the butt. We used a few gauges that read a laser beam, and also the basic probe which reads air flow around it as it moves thru the bore (these are good for about .00015"). This is mostly for size, but will also show you a drift in the bore or out of roundness. I also built gauging complexes that would check every spec on the part including concentricity. Many of these used electronic probes that never actually touch the part. These things are good for less than .0001" variation. But the best one I ever saw in use was a simple ultra sound setup used in a military ap. I thought it was a joke at first, but soon learned it was very reliable and also very quick. All it did was measure wall thickness on a given sized O.D. We used that one on the biggest gun of them all (65")
    gary
     
  7. Trickymissfit

    Trickymissfit Well-Known Member

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    There's a gauging company (name escapes me at the moment). They sell this machine that is pretty much a custom built one for each application. You simply lay the shaft in two vee blacks that are roughly 20% in from each end. There are two tail stock affairs that use a special centering device on each end. They sorta grab the part and rotate it two or three turns in clockwise and counter clockwise directions (the reverse rotation is key). While the shaft is being rotated a vertical probe comes in and checks for runout, and locates the highest points. It then sets the shaft back down in the vee blocks (these are not conventional as they have radiused surfaces contacting the parts). The secound head will then come in and apply pressure where it's needed to make the part strait (uses a ball screw with an encoder and a device to actually measure applied pressure). It rarely has to check the part three times, and will usually be in the five tenths range when it releases it. The machine is programed to toss out parts that are warped too much (around .025"), and parts that will not straiten after five attempts. We had them big enough to do 4340 shafts 1.5" in diameter over 40" long. But most were in the 20" to 24" range.

    Most people don't realize that you can have a piece of steel perfectly strait, but when you start cutting metal it will go all over the place. EDM is not so bad, but a mill or lathe operation will change it. Nature of the beast!
    gary
     
  8. J E Custom

    J E Custom Well-Known Member

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    I have visited the barrel shops and you are right.

    Most of the problems now days come from the stress relieving process or the contouring.

    Barrel blanks are normally straight and the drilling has gotten better, But when the stress
    relieving is not set up right that will warp the barrels and when the contouring is rushed
    problems will occur.

    At one barrel shop the operator was taking the excess material off in 2 cuts in order to
    speed up production I had some issues in the past with barrels with run out (Not straight)
    and wanted to see is I could spot the problem because I was having to turn the barrel
    down to true it.

    After speaking to the shop foreman I was told that this was the way they had allways done
    it and I was to picky (A good possibility) but I get other barrels that are straight from other
    makers.

    The long and the short of it is, that I no longer buy barrels from him.

    I check all barrels between centers (End to End) and measure Total indicated run out.

    Start with a good barrel and the outcome will be good !!!

    J E CUSTOM
     
  9. 21buck

    21buck Well-Known Member

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    JECustom, Trickymissfit, rscott5028, I appreciate the great effort it took to write up these explanations. I always wondered how can we shoot straight if we don't know that the barrel is straight.
    I know a lot more than I did before your assistance. However, I still have the basic question: How to straighten a barrel? A good example a friend has a barrel that is concentric on the external but has shadows within the length of the bore? JE Custom recommended that a barrel out of spec be returned. I just don't know if it is out of spec. Quandary : Ask the manufacturer to stand behind his work? or go thru the work of chambering and fitting, and acutal firing to tell the manufacturer that his product is questionable and we want it replaced with one of quality? My diplomacy is not the best but the manufacturer is the responsible party at this point. We cannot afford to reinvent the straighting process. Please advise.

    Thanks for all your help so far. Have a great Holiday.
     
  10. Trickymissfit

    Trickymissfit Well-Known Member

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    I've seen some pretty ugly barrels shipped in the past, so it's a good thing to check them out. I remember Bill Calfee once said that he only uses two out of five custom barrels he orders!
    gary
     
  11. J E Custom

    J E Custom Well-Known Member

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    If the barrel is straight on the outside but has "Shadows" on the inside you would have to prove
    it was not straight or just ask the barrel maker if he could re check it. Most of the good barrel
    makers don't want a bad barrel out there and would be more than happy to check it out to see if
    they have a quality control issue.

    I would not think an individual could straighten or afford the equipment to straighten a barrel
    and in the case of a questionable barrel most good smiths are not willing to take the chance
    and use it if they have any accuracy guarantee. and if the barrel maker does not replace or
    verify the quality of their barrels I never buy another one from them, and end up eating the
    cost of the barrel in lieu of taking the chance of building a Turd.

    The barrel is a small portion of the cost of a custom build, but a major portion of the total
    accuracy potential of any firearm.

    The best smith cant make a truly accurate rifle if he does not have a good barrel to start with.

    So confirm that its a bad barrel or replace it, would be my advice.

    J E CUSTOM
     
  12. rscott5028

    rscott5028 Well-Known Member

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    My apologies because this doesn't address the OP.

    But, Gordy Gritters talks at length about dialing in your bore in his DVD, Chambering Championship Match Barrels on a Grizzly Lathe. He pretty much comes right out and says that NONE are straight and says the method he uses seems to account for that.

    I wonder if he tosses out more barrels than he seems to indicate.

    I need to watch the DVD again more closely.
     
  13. blipelt

    blipelt Well-Known Member

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    not to change the subject

    Doesn't most gunsmiths stress the barrel blank a little when dialing in and chambering?

    Brent
     
  14. J E Custom

    J E Custom Well-Known Member

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    Not at all.

    All of there processes are done at ambient temperatures and in the case of reaming very
    little material is removed at a time while cutting the chamber(.015 to .030 Thou and clean)
    if they don't have a flush system. If they do more can be removed without cleaning but
    a light cut is made to save the reamer.

    J E CUSTOM