Blue printing question? Lapping

Discussion in 'Gunsmithing' started by foreign, Jul 17, 2014.

  1. foreign

    foreign Well-Known Member

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    So I just got done blue printing my first action.(700) what a lot of tool making time vrs cutting time!!
    When I color he back of the bot lugs and test them in he action I get what I think is perfect even wear. That's just holding he action upright and letting the weight of the bolt hold pressure down on the lugs. Once I put the firing pin assembly in though I just get one lug contacting. Concern? Do people test for contact with the pin in?should I sleeve the bolt? Should I lap the rings in?
    Thanks
    Ps. Forgot to mention that's with the trigger in.
     
  2. DakotaFire101

    DakotaFire101 Member

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    I made a mock barrel about 6 inches long out of steel threaded for a 700 action and recessed for the bolt nose then basically chambered it for a 7/16 diameter spring leaving about 1/4 inch of the spring sticking out of the "breach" then thread your action on with the recoil lug insert bolt and you should have plenty of tension holding the bolt tight in the receiver. Simply holding it upside down ain't gonna do it for ya
     

  3. DakotaFire101

    DakotaFire101 Member

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    And not sure how your checking for contact but I use a dirty flame and hold the bolt a couple inches above it til it gets a good layer of soot on the back of the lugs then check it with the receiver
     
  4. foreign

    foreign Well-Known Member

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    hey Dakota
    think you miss understood my question. or i wasnt too clear. i know how to lap. just i have 100% lug contact without the firing pin mechanism in the bolt but once i put the mech in the trigger raises up the back of the bolt and i loose contact with one lug.
    so my question was should i lap it in for that. just not what it seems like other people do.
    cheers
     
  5. Hired Gun

    Hired Gun Well-Known Member

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    foreign,
    Your observations is spot on for a perfectly trued rifle. When the bolt face and lugs are all trued to the bolt raceway, only the bottom lug will touch with the firing pin and trigger are installed. If you lap it to bear evenly on the lugs when cocked you will be at least .001" out of square. Yes people check this all the time and will ask about it. Leave it alone and finish the rifle. I have to explain this to almost every custom rifle customer that is receiving their first custom.
     
    Last edited: Jul 17, 2014
  6. foreign

    foreign Well-Known Member

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    thanks Hired Gun
     
  7. stenger

    stenger Well-Known Member

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    Bolt slop is what causes the top lug to pull away. The trigger pushes up on the bolt which has slop thus causing the bottom lug to act as a hing or pivot point. sleeve the bolt and lap only the bottom lug. I had one rifle go from a .4 to a .2 gun just by getting both lugs to touch on a trued receiver. That action had around .018 of slop on the bolt. Or get a PTG bolt and spec the size bolt body to get rid of the slop.
     
  8. J E Custom

    J E Custom Well-Known Member

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    Not sure how everyone else does it, but first I square the contact surface with the bolt set up in the Lathe (Only enough to clean them up).

    Then while truing the action face I also square the receiver recoil lugs then everything is square to the world.

    The lapping is done to smooth the surfaces to aid in bolt lift and should be held to a minimum to prevent removing to much metal on one lug or the other.

    I set head space and lug contact without the firing pin assembly and the ejector plunger in the bolt
    to prevent a false reading.

    If everything is done right, when a round is chambered and fired everything will be if perfect alignment (At least as much as possible).

    Simply Lapping the lugs does not square them, it only gives them more contact surface.

    Just the way I blue print an action.

    J E CUSTOM
     
  9. Hired Gun

    Hired Gun Well-Known Member

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    JE,

    I believe you single point your action tennon threads to clean them up to assure alignment there too. Your way is how it's done here too.

    What Stenger is recommending will throw the bolt face and lugs out of square. Even the tightest custom actions move enough that the top lug unloads a bit while cocked. By neck sizing the bolt will be held back against the lugs and during firing everything will remain in perfect alignment.
     
  10. J E Custom

    J E Custom Well-Known Member

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    Yes, the threads need to be trued while in the lathe because most may have tapered threads and as the barrel makes up they may get tighter or looser. if anything it removes all of the dope they apply
    when they barrel up an action also.

    The industry uses lots of taps instead of single pointing them and the fit is not as good as it should/could be. Lots of muzzle brakes are taped also and have the same problem.

    J E CUSTOM
     
  11. stenger

    stenger Well-Known Member

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    Your right even custom actions have some slop. Most bench rest actions are around .002 bolt clearance. When they unload its a very small amount and most maintain light lug contact. Now if you have a bolt with .018 thou of slop the top lug is gonna unload a lot! Since a lot of people including me don't like sticky bolts we full length size with about .001--.002 shoulder bump. Even with a neck sized snug fit case your still going to have some bolt lean thus causing the top lug to pull. So during the firing process the bolt falls and get slammed back into the lug seats thus causing vibrations and other unwanted movement in the action. If you have a sloppy bolt it's going to lean causing the bolt face to also lean. So you have to remove the bolt slop as much as possible. In a hunting rifle around .005 of bolt slop is good. Now when you chamber a round the top lug is gonna pull away just a little bit thus causing the bolt face to lean just a little. Most people don't worry about it but if you wanna squeeze every bit out of the action you must lap the bottom lug until the top lug touches. Your only going to lap it a tiny amount (.001)and the top lug will come in. Your action was only true when the bolt was under no stress. The trigger group will cause bolt lean and now you have a true action with a crooked bolt and bolt face due to bolt lean. sleeving the bolt and lapping the bottom lug only causes the bottom lug to be .001 shorter than the top but now it makes the action face, case head, bolt face and full lug contact square. So nothing is out of square just one lug is a tiny bit shorter than the other. I don't like to put names on the net but I was taught this technique by a very famous well know accuracy smith that chambers a lot of winning rifles out of his shop near Kanas City Missouri. I having been using this technique for a few years with great success! Everyone has a different way of doing things ex specially when it comes to rifles. I like my method because it reduces bolt lean, reduces bolt face lean, reduces bolt slop, reduces bolt fall, reduces vibration, and causes double lug contact. Which in turn causes my rifles to shoot tiny little holes in the paper !!


    Good shooting.
     
  12. foreign

    foreign Well-Known Member

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    lots of good info here. thanks guys

    Stenger
    what your saying makes alot of sense to me. my action rear bridge measures.702 and my bolt is .6955.
    So how do you lap it in while keeping the rear of the bolt against the top of the action so that just the bottom lug is lapping?
    or do just put lapping compound on the bottom lug?
     
  13. stenger

    stenger Well-Known Member

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    Lap it with the trigger installed and only put compound on lower lug. Be careful it only takes a little bit.
     
  14. stenger

    stenger Well-Known Member

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    Also remember that on a chambered barrel this will change your head space. Make sure you clean it up very good