excessive primer pocket depth?

Discussion in 'Reloading' started by gspman, Jun 7, 2012.

  1. gspman

    gspman Well-Known Member

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    What would be a good rule of thumb in regards to primer pocket depth?
    I am reloading "once fired" .280 brass and 4x reloaded .300wm.
    In both lots of brass i am seeing some pocket depths exceeding .0133, some up towards .0144.
    I am trying to determine at what depth to start throwing brass out?
    I am guessing ~.0132 would a good limit....not sure though
     
  2. Mikecr

    Mikecr Well-Known Member

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    You mean .133-.144"
    The Sinclair large primer pocket uniformers go to .133"

    You need them all the same depth. I would pick a depth I could uniform.
    So IMO, 0.133 max
     

  3. kaseyfied

    kaseyfied Well-Known Member

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    pretty sure its .128 to .132... thats what I have always herd and thats what I use for all my rifles from 25wssm to 338 lapua mag.. they say best seating is with primer .001 to .002 from top of pocket.. my pockets are at .130.. and I get great results and very consistant velocities so I must be doing something right lol
     
  4. flashhole

    flashhole Well-Known Member

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    You will find out how deep is too deep when you pull the trigger and get a light primer strike. Instead of "Pow" you will just hear "Click". Time to throw that one out. I try and keep my primers seated just below flush to the bottom of the case. .002" - .004" works for me.
     
  5. Mikecr

    Mikecr Well-Known Member

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    A while back I was handed an opportunity to see that primer striking is way bigger than talked about.

    My son's Cooper started throwing big fliers. This was a solid 3/8moa gun that seemed to drift off into 3/4moa. And it was a gradual, but abstract change.
    I chased my tail on it for over a month, swapping scopes, checking bedding & action screw torques, checking max OgvOAL. I changed bags, tried different barrel cleaning & fouling. I disassembled the bolt a couple times and found no issue, and went into the trigger, no problem.
    The gun just stopped shooting well, as it was triple grouping. That is, if I fired 10 or 20 shots at a single bull, I would end up with 3 relatively normal groups separated from each other, and they didn't walk there in order but randomly landed into one area or another & back.
    Also, ES was higher than I'd ever seen from the load, and I knew there was no aspect of my ammo that had any issue. This put primer issue in the back of my mind(bad lot?) Couldn't prove it..

    One day I got lucky as hell; a misfire. About 30 shots later, another misfire.
    Back at the bench I measured the fired firing pin protrusion, cycle, dry-fire, remeasure(bunch of times). Found that my pin was intermittently slipping through it's set-screw in the cocking piece, resulting in several protrusion distances.
    I had pulled on the pin earlier while checking the bolt, but my scrawny little pull check didn't get it..
    Start over, where should the pin be set?

    Back to the range with a bunch of tools and my standard load. Tweak the pin setting 5thou protrusion at a time & firing groups. Took a while to home in on it, but I ended up with one setting that was better than all others -with that primer -and my standard seating(3thou crush in uniformed pockets).
    With this info I went back to the bench and dimpled the pin to put it on the magic setting, and double set-screwed it -with locktite!
    Now my kid's Cooper shoots solid 1/4moa and no more mystery fliers.

    If I had never seen the gun shoot better,, if it had come to me shooting with this problem,, I never would have had any luck with the gun. I would have assumed it needed a better barrel. Then when that didn't work, I would have separated the gun into several dumpsters and been done with it.
    Now I have a lot of things to test and learn about primers & striking of them. I should be out there doing it today!
     
  6. flashhole

    flashhole Well-Known Member

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    That's an interesting post Mike. Did you notice differences in the primer strike indentations on the primer itself?
     
  7. Mikecr

    Mikecr Well-Known Member

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    No, the indentations were exactly the same, even with misfires.
    There are at least two relative aspects/approaches to primer ignition; Speed and/or Power

    You can crush primers flat in a vice, slowly, without setting them off(but not always).
    As mentioned if the pockets are too deep, and primers not seated in contact with pocket bottom, you get misfires. This, even with normal indention.
    I believe the primer compound lead styphnate requires more shock, than force, to set it off.
    SPEED

    How a primary explosive can vary in it's ignited performance is totally beyond me.
    I used to think that once ignited, even if 'barely', it's output would be the same.
    Now I know this isn't true at all.
    But I don't understand why.