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Thread: Problem with primers backing out.

  1. #1

    Default Problem with primers backing out.

    .257 Roberts. New and once fired Remington brass and CCI 200 primers. IMR 4320 and 100 gr. Sierra SPBTs. Doesn't matter what charge I put in them. Low end all the way to just under max the primers back out the same in all of them. Haven't actually measured but just by looking at them they look the same. Accuracy is very nice with this load at 38.5 grains. Why would the primers move like this? They didn't with the 40 rounds of Hornady factory loads I've put through it. Will be trying WLR primers next.
    Is it even a problem if everything else is working right?

  2. #2
    Member Big Al's Avatar
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    Quote Originally Posted by idahoducker View Post
    .257 Roberts. New and once fired Remington brass and CCI 200 primers. IMR 4320 and 100 gr. Sierra SPBTs. Doesn't matter what charge I put in them. Low end all the way to just under max the primers back out the same in all of them. Haven't actually measured but just by looking at them they look the same. Accuracy is very nice with this load at 38.5 grains. Why would the primers move like this? They didn't with the 40 rounds of Hornady factory loads I've put through it. Will be trying WLR primers next.
    Is it even a problem if everything else is working right?
    Take an empty primed case, chamber and fire. Did the primer back out?
    "The tree of liberty must be refreshed from time to time with the blood of patriots and tryants." (Thomas Jefferson

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    Member L. G.'s Avatar
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    There's really only one reason I can think of for your "problem."

    You're running LOW pressure AND you're "oversizing" your cases.

    Let's say you are FL sizing to cam over. That is to say, you are bottoming out the die on the shell holder. You are probably over-resizing your cases by 0.005"+.

    When you fire the case, the firing pin hits the primer and pushes the case forward until the chamber shoulder stops it. Pressure builds inside your case. It expands and grips the chamber walls. The "grip" keeps the case locked in position. The pressure inside backs the primer out until it hits the bolt face. When the pressure is higher, the case WILL expand to the chamber dimensions - e.g. the case head will be against the bolt face and the primer WILL be flush with the case head.

    Next time your resize, try backing off on your die 1/2 turn and see if the case fits. Remember 14 pitch thread are 0.007" per revolution. IIRC a 0.004 or 0.005" overlength is a NO-GO gauge length.

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    Member thebovees's Avatar
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    Default 14 Pitch = 0.007???

    If I am not having too many senior moments 1/14=0.0714". I don't take much to get over length!

    Roger

  5. #5

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    Thanks for the info everyone.
    Quote Originally Posted by Big Al View Post
    Take an empty primed case, chamber and fire. Did the primer back out?
    It did. About .005". The cases that had powder & bullet are all backed out about .008".

    I am caming over (always have cause that's what RCBS says to do) so I will try backing the die out a bit.

    Speer say 39 grains of IMR 4320 is max. At 38.5 I shouldn't have low pressure should I?

    By the way, the rifle is a 1950 Remington 722. It's in excellent overall condition.

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    Member Big Al's Avatar
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    With out knowing a lot of answers to other questions, do the test I advised. If the test results look the same, you have head space problems. You fired factory ammo with no problems. You used new brass and had problems. You did not say if you full length sizes the new brass? Small extractors as per Remington (700) do not hold the case head against the bolt face vary well. Some vary tight claw extractors won't do it either.

    Actually all primers back out of the primer pockets and push back in with set back if the pressure is high enough. Single shot actions are bad about this (some). The other post is right, you maybe pushing the shoulder back, when sizeing.

    The best way to set your die is to use case lube on the case neck, making repeated changes on the die as you size, looking for a line of lube on the neck. Screw the die down until the lube line just touches the shoulder. This is the neck size only set for that die. If you have a set of calipers you can measure the case in the die several times and wright this reading down and do an average of the reading. (bottom of the case to the top of the die body) Later on you can set the die down looking for a measurement of -.003. this is your shoulder set back point. (again from the bottom of the case head to the top of the die) Another way is by setting the die with a piece of 0.003" shim stock. You set the die up and find the same point (neck size only) You want the shoulder to bump back, you remove the shim. You get instance shoulder bump back of 0.003" set back.
    "The tree of liberty must be refreshed from time to time with the blood of patriots and tryants." (Thomas Jefferson

  7. #7

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    I did full length size.
    I will try neck sizeing only.
    Thanks again.

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    What type of rifle are you shooting?

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    Remington 722 .257 Roberts. Born July 1950.

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    Quote Originally Posted by L. G. View Post
    There's really only one reason I can think of for your "problem."

    You're running LOW pressure AND you're "oversizing" your cases.

    Let's say you are FL sizing to cam over. That is to say, you are bottoming out the die on the shell holder. You are probably over-resizing your cases by 0.005"+.

    When you fire the case, the firing pin hits the primer and pushes the case forward until the chamber shoulder stops it. Pressure builds inside your case. It expands and grips the chamber walls. The "grip" keeps the case locked in position. The pressure inside backs the primer out until it hits the bolt face. When the pressure is higher, the case WILL expand to the chamber dimensions - e.g. the case head will be against the bolt face and the primer WILL be flush with the case head.

    Next time your resize, try backing off on your die 1/2 turn and see if the case fits. Remember 14 pitch thread are 0.007" per revolution. IIRC a 0.004 or 0.005" overlength is a NO-GO gauge length.
    You're exactly right here, except it is .070" per turn, and a half turn is about right, or .035" of an inch short of bottoming out the ram. (shell holder/die contact.) This is a case of excess headspace (head to shoulder dimension). Higher pressure would stretch the case back and shove the primer back where it belongs. The cases would suffer, with this but with the less than 60Kpsi of the Roberts it just leaves the primer stickin out like a sore....thumb.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



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    Quote Originally Posted by idahoducker View Post
    I did full length size.
    I will try neck sizeing only.
    Thanks again.
    Never F/L size case unless someone threatens to beat you with your own gun barrel.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



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    Quote Originally Posted by idahoducker View Post
    Remington 722 .257 Roberts. Born July 1950.

    You lucky stiff!
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



  13. #13

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    Quote Originally Posted by Murphy View Post
    You lucky stiff!
    Thank you. I've been hearing a lot of that since I bought it. Not only did I get lucky finding it, look what it's doing for me. And that's shooting from a slightly wobbly portable bench.


    I'll be trying some properly (I hope) sized cases tomorrow.

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    Quote Originally Posted by Murphy View Post
    You're exactly right here, except it is .070" per turn, and a half turn is about right, or .035" of an inch short of bottoming out the ram. (shell holder/die contact.) This is a case of excess headspace (head to shoulder dimension). Higher pressure would stretch the case back and shove the primer back where it belongs. The cases would suffer, with this but with the less than 60Kpsi of the Roberts it just leaves the primer stickin out like a sore....thumb.
    Great advice!!! Neck size only after shooting them once and your problem will be gone

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