Thoughts from the pro's

Discussion in 'Gunsmithing' started by Mainmechanic, Apr 25, 2019.


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  1. Mainmechanic

    Mainmechanic Active Member

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    Gentlemen. From my previous posts I have said I don't claim to be a gunsmith .Spent the majority of my life in a machine shop. With that being said I can fully appreciate a square true rifle action. Read a lot about recurring action threads true to bolt raceways. My questions. 1 - could I make a fixture similar to a threaded barrel tenon and several inches of barrel that I can screw into the receiver that I could then chuck in my lathe and then cut my receiver face true to the threads ? Would save recutting receiver threads and shortening and recutting barrel threads thus changing bedding. Would also be able to drill a hole in this fixture and apply pressure to bolt to lap lugs and also recut bolt face. Any thoughts on this would be appreciated. Have more to say just don't want this to get any longer than it is. Best regards
     
  2. KyCarl

    KyCarl Well-Known Member LRH Team Member

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    Chuck up a butt and then turn the end and chase the threads. From the same chucking! That way it will run as close as that lathe is able. Taking it out and re indicating won't be as close...
     
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  3. Mainmechanic

    Mainmechanic Active Member

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    Thanks. Please elaborate more not sure exactly what you mean .
     
  4. Edd

    Edd Well-Known Member

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    Why would you want to make the front of the action true to the threads without giving any consideration to the bolt raceway?
     
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  5. KyCarl

    KyCarl Well-Known Member LRH Team Member

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    I was saying to make your fake barrel all from the first chucking. and use it.
    It will never go back as close! I made all kinds of disposable tooling for a
    lot of this and that?
     
  6. Mainmechanic

    Mainmechanic Active Member

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    I believe I understand the importance of keeping everything true to the bolt raceway. If indicating everything off of that I would probably discover action threads are not concentric to it. Would then , I presume , need the action threads recut oversize ? Among the rest not being perfect. My line of thought is the way I noted would have the barrel shoulder and action face correct . Then recut the bolt face with the same fixture ( modified ) and possibly lap the lugs . Could be completely off base . All those areas would be correct except for not matching up to the raceway ? Would not require touching the barrel and having to rrebed. Once the boltface was recut even if not true to the raceway , would this not be a manageable compromise ? Just questions here. No disrespect .
     
  7. Mainmechanic

    Mainmechanic Active Member

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    KyCarl ..Yes that is what I was thinking. Your thoughts on how this may work ? I hope I explained my thoughts correctly . As talking about with Edd there would not be any consideration for the bolt raceway . Just trying to avoid the things I just mentioned. I do realise it would not be perfect because of that but possibly good enough for my use. Thanks
     
  8. KyCarl

    KyCarl Well-Known Member LRH Team Member

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    I'm no expert but I'm looking at ways to inspect the bolt face in the Locked Position.
    Lug engagement % of face contact Exactly where it is and how it's aligned the instant the rifle fires. If one lug has good engagement say 80% full but the other has way less or isn't even touching only .001 off you couldn't feel it by cycling but when it fires in that micro millisecond there will be some flex of the face.
     
    Last edited: Apr 25, 2019
  9. Mainmechanic

    Mainmechanic Active Member

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    Good food for thought .
     
  10. Daveog

    Daveog Well-Known Member

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    I've recut several receivers. I'm not exactly sure what you are proposing, but it sounds like are trying to square the face of the receiver to the existing threads? What you need to do is cut the threads so they are parallel to the the receiver and square the face as well. The best way to do this is buy a raceway reamer from PTG (http://pacifictoolandgauge.com/rifl...9901-705-bolt-raceway-reamer-mandrel-hss.html) that you can use with bushings to have a ground surface that is completely true to the receiver body to indicate on. When you do that, you have the receiver indicated true to your spindle and when you cut threads they become true to the receiver and when you face the receiver, it is square as well. You can buy, at great expense, a piloted tap (http://pacifictoolandgauge.com/tap-mandrels/1418-remington-700-piloted-tap-mandrel-standard-hss.html) to recut the threads true to the receiver but there is a lot of debate about whether it is as good as single point threading. Bottom line is that if the threads are not in line with the receiver body, squaring the face of the receiver to the threads will still result in a barrel that is not inline with the receiver. I hope that makes sense.



     
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  11. Daveog

    Daveog Well-Known Member

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    Also, what KyCarl said about the lugs is correct. You will, ideally, need to cut those faces square to the raceway as well. Then, lap the bolt lugs to match. If you do all that, all the mating surfaces should be "perfectly" in line, giving the best odds at accuracy.

    As far as not touching the barrel goes, I think you are doing a lot of work for little gain if you mean to reinstall a factory barrel. The barrel is probably the number one place you will gain accuracy. Good chance your barrel tenon is not perfectly inline with the bore. If you get a good range rod and indicate a barrel blank to your spindle and cut the tenon inline with the bore, then the bore should be inline with the raceway when you finish the receiver. If you're going through all the effort to true the receiver, you may as well buy a quality barrel blank and thread and chamber it to match your trued receiver. Then, it won't matter how much oversize the threads are because you will cut the new tenon to match it.


     
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  12. 25WSM

    25WSM Well-Known Member

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    Learn from the best and don't look back. I will save you the frustration right now. Watch all the Gretan video series. Greg Tannel is a master at this and teaches very well also. He's a great guy and will help you in any way possible. I've been a custom Smith for 30 yrs and do all my action blueprints using his methods. And yes everything must be indicated from the center of the race way longitudinal not just at one point. Good luck if you try it any other way. Viper makes a great jig to hold your action when dialing it in. If you come to my shop I will show you how. Newcastle PA
    Shep
     
  13. Susquatch

    Susquatch Well-Known Member

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    These are actually good questions in my view because they make us all think.

    Please forgive me for rephrasing your question a bit. I think you are really asking "what is more important - mounting an existing barrel true to the axis of the receiver threads, or mounting the barrel true to the axis of the bolt?

    Of course, as others have noted there are lots of other considerations. Quality of the barrel and chambering, squareness of locking lugs, quality of existing receiver threading to the bolt raceway, etc etc

    Notwithstanding the answers you have already received with good advice from all, I'd like to say that I think it ought to be obvious that aligning all these parameters is best and that I doubt others would disagree. However, if I stick strickly to the question I think you asked, my personal guess (and that's all it is) is that the other variables outweigh the two you have zeroed in on. But sticking to your question, here are a few comments.

    A long time ago I read an article (I think it was in Rifle Magazine) by Jim Carmichael (now a world record holder) about accurizing sporting rifles in which he recommended squaring the receiver face to the threads using a lapping jig that fit the receiver threads. His thinking was like yours in as much as that would tend to square the receiver face with the threads. Someplace else around the same time I read a similar accurizing method using the barrel shoulder and recoil lug as the lapping fixture. The results in both cases were positive - groups got smaller - but still nowhere near what we can do today with a full truing treatment on a modern lathe.

    I never did try either approach myself, but they are worth thinking about and do tend to support your thinking.

    As others have said though, I personally recommend a new high quality barrel, precision threading and chambering, a fully trued action, and a high quality bedding job. If you have a lathe as you stated, why cut corners? Just do the whole job and don't cut corners!

    If on the other hand if you just want to experiment please keep us posted with your progress and learnings!
     
    Last edited: Apr 26, 2019
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  14. Gcan

    Gcan Well-Known Member

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    I think you may be missing one point.
    Thread are often on a different axis than the bolt raceway. We don’t datum off the threads. We use the raceway. We square the bolt bearing surfaces to the raceway. We machine the bolt lugs perpendicular to the bolt axis. We cut the bolt nose and face concentric and square. This makes the bolt, lugs and action bearing surfaces perfectly square. We face the action face and bolt bearing faces. Now everything is concentric.

    At this point the threads are (never found a perfect one) either eccentric to the centerline axis of the bolt and action or angularly misaligned and also eccentric. So we cut the thread bore .010 (usually enough) oversize to get the thread bore concentric and recut the threads so everything is on the same axis. We end up with a 1.072-16 thread rather than the oem 1.062-16 thread. Chamber, Bolt, lugs, action centerline, face, barrel threads are as though it was all one piece of metal.

    If you turned a old barrel blank straight and turned the tenon shoulder back. Then put the blank in a 4 jaw and screwed the action onto the blank until the face of the blank bottomed on the internal bolt bearing faces you could certainty square the action face to the thread axis but the action/bolt centerline would still not be concentric to the threads or barrel.
     
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