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Thread: Hard Bolt Lift

  1. #1
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    Hard Bolt Lift

    I've got good accuracy at 300 meters with my 6BR using Berger 105 BTs and 29.5 of Varget. However, I am also getting hard bolt lift and cratered primers. Would dropping .5 grains to 29 be enough to remedy this situation? I used to shoot 28.5 of Varget with the 105 BT with no similar problems except slightly less accuracy.

  2. #2
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    Depending on what type of action and the condition of the firing pin hole, cratered primers are not always the best indicator of over pressure. However, with fairly new brass, a difficult bolt lift is trying to tell you something.

    The flattening of the primer tells you a lot. Learn to look at the outside radius, and how much is left. These two BR cases are out of my 6BR with a 12 twist that I shoot 80 grn Bart’s out of. The one on the left is 33.2 , of Accurate 2495, the one on the right, 34.2. The 34.2 starts to have just a tad of bolt feel with fairly fresh cases. The action is a Bat Neuvo.

    I figure the left is about 52000 psi, the right, around 65,000. Notice even with the upper end load, there is no primer crater.

    If you are getting a “click” at the top of extraction, that is often an indication of brass that has been fired too many times at higher pressures and no longer responding to sizing with the die on hand.

    What type of action?


    http://benchrest.com/attachment.php?...1&d=1587426932
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    Last edited by jackie schmidt; 04-20-2020 at 08:07 PM.

  3. #3
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    Quote Originally Posted by jackie schmidt View Post
    Depending on what type of action and the condition of the firing pin hole, cratered primers are not always the best indicator of over pressure. However, with fairly new brass, a difficult bolt lift is trying to tell you something.

    The flattening of the primer tells you a lot. Learn to look at the outside radius, and how much is left. These two BR cases are out of my 6BR with a 12 twist that I shoot 80 grn Bart’s out of. The one on the left is 33.2 , of Accurate 2495, the one on the right, 34.2. The 34.2 starts to have just a tad of bolt feel with fairly fresh cases. The action is a Bat Neuvo.

    I figure the left is about 52000 psi, the right, around 65,000. Notice even with the upper end load, there is no primer crater.

    If you are getting a “click” at the top of extraction, that is often an indication of brass that has been fired too many times at higher pressures and no longer responding to sizing with the die on hand.

    What type of action?


    http://benchrest.com/attachment.php?...1&d=1587426932

    Mr. Schmidt:

    Here's a picture of two shells fired today. Nothing fancy about this gun-strictly a benchrest wannabee for me to shoot as small as groups as possible despite the Kansas wind and mirage. The rifle is a Savage I rebarreled with a Pac-Nor barrel and installed an aftermarket trigger. By the way, those are Federal Match primers which may explain some of the cratering since I understand they are softer than usual. The brass has had 6 or 7 firings.
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    Last edited by Jayhawker; 04-20-2020 at 10:06 PM.

  4. #4
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    Any chance that you're sizing the body/shoulder of the brass too much? There seems to be a lot going on with the base of those cases. The circular mark mid rim is unusual; the neat junction between primer & case could suggest pressure but equally be the result of the primer exiting the case a tad because the latter is too undersize for the chamber then riveting back when the case expands.

    On balance, though, I'd be inclined to say that your load is too brisk for the conformity of your chamber & throat and your firing pin could stand bushing.

  5. #5
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    Quote Originally Posted by John Kielly View Post
    Any chance that you're sizing the body/shoulder of the brass too much? There seems to be a lot going on with the base of those cases. The circular mark mid rim is unusual; the neat junction between primer & case could suggest pressure but equally be the result of the primer exiting the case a tad because the latter is too undersize for the chamber then riveting back when the case expands.

    On balance, though, I'd be inclined to say that your load is too brisk for the conformity of your chamber & throat and your firing pin could stand bushing.
    I set my sizer based on how the shell feels as I chamber it. This has pretty faithfully resulted in .001"-.002" pushback on the shoulder and a very slight drag when chambering. In shooting 28.5 grains of Varget instead of the 29.5 I was firing today, I have very slight cratering and no bolt lift problems. I'll look into the firing pin bushing.

    Thank you for your reply.

  6. #6
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    Quote Originally Posted by Jayhawker View Post
    I set my sizer based on how the shell feels as I chamber it. This has pretty faithfully resulted in .001"-.002" pushback on the shoulder and a very slight drag when chambering. In shooting 28.5 grains of Varget instead of the 29.5 I was firing today, I have very slight cratering and no bolt lift problems. I'll look into the firing pin bushing.

    Thank you for your reply.
    O the looks of those primers, you have too much firing pin to hole clearance.

  7. #7
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    Quote Originally Posted by jackie schmidt View Post
    O the looks of those primers, you have too much firing pin to hole clearance.
    Thanks for the reply. The bolt is coming apart right now.

  8. #8
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    Primers appear to be flat, no radius around the edges. If the truly are, the load is hot!

  9. #9
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    Feb 2019
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    I’ll agree with Jackie on this one. The firing pin hole needs a bushing job. Step one is to take the bolt apart and clean out the firing pin area real well. If that isn’t very clean the bolt needs to be sent out to be bushed. The primers are trying to tell you this. Also, if those cases have five or six firings on them the printing on the base are not hammered out.

  10. #10
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    Quote Originally Posted by steve stanley View Post
    Primers appear to be flat, no radius around the edges. If the truly are, the load is hot!

    I agree with Steve on that one. Under this angle of view, primers appear full flat, and furthermore, it seems to me that some bolt face machining got inprinted onto the case head. (or primer pocket cleaning tool imprint ???)


    Before going to bushing I would :

    check the inprints on case head looking at bolt face machining
    check the firing pin head diameter and the FPhead hole in the bolt face for clearance and make sure bushing might be needed.


    This could also be a weak spring loaded FP. Despite "regular" pressure, the FP is pushed back because of a weak spring or a non adapted load from the spring on the primer cup under pressure.

    Should you had pierced primers by the past and/or misfire occuring, check for primer cup debris inside FP channel in bolt, leading to misfire and too short FP protrusion.


    Or, the load is so hot that a) imprint of bolt face on case head b) FP is pushed back inside the bolt because of excessive load pressure, thus primers are cratering.


    Anyway, I do not like the aspect of your primer cups. Check them at an angle. If the radius has fully turned to a sharp angle or even an expansion into the primer pocket chamfer, you are too hot.

    Hope this help.

  11. #11
    Join Date
    Feb 2006
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    Wilcox, PA
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    Check out primer

    Maybe primer didnt seated far enough in that has happen

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