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Thread: Primer depth

  1. #1
    Join Date
    Nov 2008
    South Carolia

    Default Primer depth

    I understand that the primer is a very important part of cartridge assembly, and have done considerable searching on the net for proper seating data. The most accurate answer I have found is the the base of the primer should be .005 below the base of the cartridge. Is this correct, or is it caliber specific?

    Or, am I being way too anal about seating the primer?

  2. #2
    Dogs Like Him versifier's Avatar
    Join Date
    Dec 2005
    New Hampshire


    Welcome to the Guide lesterg3.

    No, it is not caliber specific. Primers need to be seated just below flush, but not so deeply that the priming pellet is crushed. I think .001-.002" is plenty to prevent the bolt face from hitting it. I suspect that .005" is too deep, though I do not know if it is enough to kill the primer. When a primer is seated by feel to the point where it just bottoms out in the pocket, it is below flush and undamaged, but I have never actually measured it to know exactly what the numbers are. Your fingertip can detect a difference of .001", though your eye cannot, so by running it over the seated primer, you can tell if it is not deep enough, if it is flush, and if it is OK. When I adjust a priming tool I start high, then bring it down to flush (check it on a hard flat surface), then go just a smidge more until I can feel it is no longer flush with the case head. Not every priming tool is adjustable, and not every system gives you enough feel to really know what is happening with it. I prefer a Lee AutoPrime2 mounted on a small Lee Reloader Press. It is fully adjustable, and the light press still gives me good feel through the operation. This is redundant, but it acts as a double ccheck and gives me confidence so I don't have to worry. I have crushed primers seating them on large presses with frame mounted and ram-type tools and also on hand held tools by getting a bit too enthusiastic, but no such issues with the AP2. The one I'm using now is approaching 20,000 rounds and only the box is showing any wear.
    "Stand your ground.
    Do not fire unless fired upon.
    But if they mean to have a war let it begin here."
    - Capt. Parker, Lexington Militia, April 19, 1775

  3. #3


    Good morning I bottom mine out. If they are not on the bottom then they have to move to the bottom of the primer pocket and you may have a hang fire. I use the hand operated Lee primer tool and with single thumb pressure seat my primers down here. Not all brass is the same. But al primers need to be seated far enough so the firing pin is not first PUSHING the primer into the case before igniting the mix.

  4. #4
    GunLoad Trainee
    Join Date
    Nov 2008

    Default primers

    I always use thumb nail to feel if its seated far its worked.I also use lee ram prime

  5. #5
    GunLoad Trainee
    Join Date
    May 2008
    SE Virginia

    Thumbs up Primer Depth

    lester3g, primer pockets are divided into three groups;Small rifle/pistol, large rifle, and large pistol.

    Small rifle/pistol minimum depth should be .117 inch, maximum depth is .123 inch.

    Large rifle primer pocket depth should be .125 inch minimum, and .132 inch maximum.

    Large pistol primer pocket depth should be .117 inch minimum, and .123 inch maximum.

    The rounded corners of primer pockets should be squared up (cut) for best accuracy and safety. Different depth primer pockets will result in varied powder ignition, and vertical shot to shot dispersion at longer ranges.

    Safety is also a major reason to uniformly cut your primer pockets, especially with tubular magazine rifles, so the primers are not pushed against by the bullet loaded behind it, and on semiautomatics, especially the M 14/M1A rifles.........they have a floating firing pin, that can cause slam fires, if the primer sets up too high, ESPECIALLY if using the softer Federal primers.

    Since you have to clean primer pockets anyway, rather than use a primer pocket brush, get a primer pocket uniformer, which will clean the old residue out, AND cut the primer pocket to it's best depth.

    You can get a primer pocket uniformer from Sinclair International. Easy to use, just like the brush, but with a cutter and depth gauge stop, that prevents you from cutting too deep.

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BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
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