Gordie Gritters - bbl centering

Discussion in 'Advanced Gunsmithing & Engineering' started by Bob3700, Jan 23, 2009.

  1. Bob3700

    Bob3700

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    Gordie,

    I watched you segment on centering bbls in the lathe with your indicator rod. The concept made sense to me. Get the end of the bbl you are indicating, straight for two inches.

    Now it practice, I have a question for you.

    I got the muzzle of my SS cut rifle bbl in the chuck with the breech end thru the spider. Centered the muzzle up for two inches using your technique in the video with an indicator rod from Kiff. Once that was finished I looked at the breech end sticking out the spider. It was running in a rather pronounced elipse. It that what is supposed to happen here? It would seem that in order to have the muzzle run true for two inches, I am putting a pretty good strain/bend on that bbl to get it to indicate true. What happens once I take it out of the lathe? The true will be gone!

    In the past I have always indicated the muzzle and breech in at the same time,to the centerline of the lathe) and always had outstanding results on target. This new method is one that I don't understand how it would contribute to accuracy.

    Please let me know what I am doing wrong.

    Bob
     
  2. tightneck

    tightneck Gold $$ Contributor

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    "In the past I have always indicated the muzzle and breech in at the same time,to the centerline of the lathe) and always had outstanding results on target. This new method is one that I don't understand how it would contribute to accuracy."

    Then why would you want to change????????
     
  3. Bob3700

    Bob3700

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    Tightneck,

    Always exploring better ways to improve my on-target performance.

    If someone has a better way to center the bbl up, I am all for it.

    I'll try different techniques and compare them with what I am doing. If you don't experiment, you don't learn.

    Bob
     
  4. wnroscoe

    wnroscoe

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    In the video, the method Gordy uses is almost the same as using a Pioleted Range Rod from PTG and dialing in using two points on said rod. Using the Range Rod method, when the breech end is true, the muzzle end will be running out. To crown, you simply swap ends and repeat the process. There's more than one way to chamber a barrel. I try my best to have the bullet enter the throat / lands straight and leave the crown / muzzle straight.
     
  5. tightneck

    tightneck Gold $$ Contributor

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    Bob, I am an experimenter by nature, so I know where you are coming from. From your earlier post, it sounded like you didn't feel like you had much room to improve with your chambering technique, as far as on the target performance. I dial in the future throat on the grooves, and do the same on the muzzle end. I single point bore most of the chamber, finishing with only a few passes with the reamer. This is the method that I've come to rely on, and it has served me very well, as well as many others. I'm not saying that other methods won't work just as well, but judging by TIR and on-target performance, I don't think this method can be improved upon. After a perfect chamber job, its all on the shooter...oh, and the quality of the barrel.
     
  6. Rustystud

    Rustystud Site $$ Sponsor

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    As I have stated before there are many ways to skin a cat.

    As all barrel makers will tell you rifle bores are deep drilled and are not prefectly straight.

    Good drill geometry makes for straighter holes.

    Reamers make rifle bores closer to being round.

    Lapping makes them smoother and can aid in making them more consistent in diameter.

    Buttoning or cutting the rifling has its own effects.

    The addition of stress releiving before, during and after these aforementioned processes removes some induces variables.

    Most of the better rifle barrel makers can make a hole in a barrel that is within .0003 in diameter for at least 30 inches.

    I have set back barrels that were previously done by Gordy Gritters and the machine work he does is second to none.

    I have used his technique and that of Greg Greg Tannel both very accomplished gunsmiths.

    I have done it the same ways as described by Ed Shillen and Butch Lambert.

    I have done it the same as Mike Bryant, and Speedy Gonzales.

    I am not sure that there is any one way that is better than another.

    The wonderful thing about gunsmithing is that we all experiment a little and the ones that have better results usually get duplicated by the others.

    I was told by one of the top barrel makers that the first few inches of a new barrel made by the top barrel makers is so straight that less than .000005 could be measured over a 4 inch length. Most gunsmiths and machine shops don't have the means to read the deviations in millionants,sp).

    Using piloted rods are accurate enough for target rifle accuracy but are not as accurate as true pin gauges due to their variablility in bushing and bearing surface tension.

    The bottom line is what ever method we use we all strive to do the best we can. An in most cases that is far superior to what is found in factory rifles.

    Rustystud
     
  7. GordyGritters

    GordyGritters

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    Bob, Depending on how straight the bore is in the barrel, when you get the end you are working on running straight and true, the other end will be running out a little. Normally it isn't by much, but I've seen them as much as .020" off center,.040" TIR) in heavy match barrels, and even a little farther in slender hunting barrels. None of that is a problem if the bore at the end you're working on is running perfectly straight.

    I've been teaching some custom chambering and gunsmithing classes at my shop for some time now, and I've really learned from some of the students as well as in forums like this how this concept is coming across, and hopefully I am finding better ways to teach them how to do this to get the best results.

    One thing I do, and I'm not sure it's in the video, is every time I make an adjustment with the outboard spider, I go back and loosen the main chuck jaws to take the tension off the barrel. Then I tighten the jaws back up very carefully to dial it in again - just "finesse it" in - most guys I see try to force it in to get the reading they want and this bends the barrel quite easily. I go back and forth making these adjustments and relaxing/re-dialing it in until the first 2-3" ahead of the crown or the throat is running straight and true, and the barrel is not forced into this position, but is held there relaxed. Then you won't see near as much elliptical runout on the outboard end.

    I use the range rod with a close fitting bushing to be able to reach quite a ways into the bore ahead of the throat, which cannot be done with Deltronic pins. But something that I'm not sure I got across in the video is after I get the pre-chamber hole drilled, I can then reach in and "fine-tune" it with my long reach indicator to make sure it is running as close to .0001" as possible both at the throat and as far ahead of that as the indicator tip will reach. As Rustystud points out, the range rod has clearance between the bushing and the rod, and the bushing and the bore, so it isn't an absolutely perfect fit. But it is normally so close that when double-checking with the long reach indicator, I almost never have to "fine-tune" it more than .0001"-.0002" to bring it where I want it.

    Hope this helps!

    Gordy Gritters
    www.gordysgunsmithshop.com
     
  8. Rustystud

    Rustystud Site $$ Sponsor

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    Gordy:

    In this last post I think you have answer many folks question about the muzzle ends being out,.020) .040 out tir. I think many thought the muzzle was out maybe .5. There is a huge difference. Your muzzles are really not out that much taking in the length of the barrel.

    It would be interesting for you to take two duplicate calibers and makes of barrel. Chamber one indicated as you do and the other with the chamber and muzzle indicated .000 I would bet a pay check that both would group eaqually as well. The only differences would be cosmetic and that is so small one would not see it with the naked eye. The reason I would bet on this is that I have already done it. I did it to an extreame test. I have a customer who every year sends me 25 barrels of the exact same make,caliber,twist and length. The are all chambered to fit the same action. He shoots the same test load in all 25 barrels and keep the 3 best for his upcoming season. He had no idea what I did and I numbered each barrel. He did his testing and brought me the targets with the groups identified by barrel numbers. His test consist of shooting 10 shot 100 yard groups with a heavy rail gun. His weather conditions and temperature are pretty consistent. The barrel maker is a well known in the shooting community. If a barrel shoots a 10 shot group greater than .3 after,break in) having fire 20 shots and cleaned between shots he culls that barrel. When he had gotten down to his top 3 barrels 2 were chambered with the muzzle and chamber both centered and 1 was chambered with the muzzle out of center by .003. I would bet if I repeated the same test it could have ended just the oposite. When he was down to 12 barrels in the test the devide was about equal. Granted there could have been some human error on mine or his part.
    Keep us informed
    Nat Lambeth
     
  9. Bob3700

    Bob3700

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    Gordie and Rusty,

    Thanks for your replies.

    You are right about different ways to skin a cat.

    I too will pre-drill my chambers and then bore them true to the throat area of the bbl.

    Gordie, you seemed to confirm my thoughts that you could use a range rod with snug bushing to go in past the pre-bored chamber and indicate the throat in for final chambering.

    Nathan, you are correct in the experimental nature of gunsmithing. Many different roads will get you to the same destination.

    Thanks for your input and thoughts fellas.

    RGDS

    Bob
     
  10. dennisinaz

    dennisinaz

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    "Centered the muzzle up for two inches using your technique in the video with an indicator rod from Kiff."


    Bob, in the video/DVD, he centered the breach for 2", not the muzzle, he let the muzzle fall where it had to to make the breach perfect. I don't know if that was a typo or if you were doing it backwards.

    Dennis
     

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