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Measuring primer seating depth.

Discussion in 'Handloading and Reloading' started by Alabama2010, Apr 23, 2010.

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  1. Alabama2010

    Alabama2010 Member

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    To preface the following, I just want to state that I don't have any kind of primer seating issue so I'm not looking for advice exactly. I've read many posts where people make references to measuring their primer seating depth and was wondering how they did it.

    I personally seat my primers as far in as they'll go. Looking under a magnifying glass, I can see that they seat a little below the bottom of the case. That simple observation is all I can do.

    How do you quantitatively measure the seating depth with calipers? Or is there another tool that's used? Seems to me that using standard calipers would leave a huge margin for error. Additionally- is it even necessary?
     
  2. Dave P

    Dave P Member

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    The lower end of all calipers are designed to measure depth (AFAIK). I stick that tailend on the primer, and the two main legs/scales on the case head . Simple.

    Maybe not accurate, but good enough for most of us.
     
  3. rcmodel

    rcmodel Member in memoriam

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    I fail to understand how measuring would tell you anything useful.
    Unless all you used were match prepped cases with uniformed primer pockets.
    And all the primers were from the exact same lot number.

    What is important is that every primer is seated fully to pre-load the anvil into the compound, and every one is seated below level with the case head.

    I do that by feel with an RCBS hand primer tool when seating.
    Then run my finder over each one to make sure it isn't sticking up.

    What each one actually measures in thousandths of a knats azz is meaningless to me.

    rc
     
  4. The Bushmaster

    The Bushmaster Member

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    By feel...As I remove them from my Lee Auto prime II I run my finger over the primer and it tells me if the primer is below the case head.

    If you lay two different thickness paper side by side and run your finger over them you will find that you can feel the difference of less then .001 of an inch.

    I also SEAT my damned primers...
     
  5. Asherdan

    Asherdan Member

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    I do the same as Dave P to check 'em. If I remember right (which means you might want to check your ownself), the recommendation from Lyman's 48th was .004" depth. I use a hand tool to seat primers so I have a good feel for them being well in the pocket, I've had some brass that won't let the primers seat that deep but firmly seated and at least .002" deep on a spot check with my calipers has been my minimum guide.

    Of course, I did that when I was starting out so I'd know what I was seeing and feeling measured within the recommended spec.

    Now I fully smoosh them in and run a finger over the pocket to make sure it feels right and carry on, as rc and bushmaster say.
     
    Last edited: Apr 23, 2010
  6. The Bushmaster

    The Bushmaster Member

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    Darn it! rc...Take a coffee break so I can beat you to the posting...Either that or type slower...
     
  7. Walkalong

    Walkalong Moderator

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    .Same here.
     
  8. Jesse Heywood

    Jesse Heywood Member

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    Using a 6" caliper to measure the depth of a seated primer is an exercise in futility. To get an accurate measure you need to use a depth gauge micrometer. But it isn't necessary, unless you are needing bench rest accuracy.

    I used to use my fingertips, but recently found that mine are not as sensitive as they used to be. (Must be due to the computer!) So I came up with a nail test. I run the cartridge head over the end up the nail on my forefinger or thumb. If the nail hangs on the primer, it gets rejected faster than the geek asking for a date with the homecoming queen.
     
  9. JimGun

    JimGun Member

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    Whether you measure or feel, the primer must be below the case head. I lost all my reloading equipment in Hurricane Ike and when my new hand loader came, I found myself having to pull the trigger twice before the round would fire. I had never incurred the problem before and was “advised” that I wasn’t seating the primer enough. I talked to RCBS and they suggested that the problem may be that the link follower in the hand primer was too short an sent me another one, free of charge. That corrected the problem. However, ever since I always feel the primer once seated.
     
  10. MachIVshooter

    MachIVshooter Member

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    This:

    I have never measured primer seating depth. It's easy to tell visually if they're not seated at least level with the case head, and that's the only time it can be problematic. Otherwise, with a hand priming tool, you can definitely feel when they hit home. I give 'em just a little more squeeze after I feel that to be sure.
     
  11. bds

    bds Member

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    I used to seat the primers in the progressive press - I thought if they were flat with the case bottom, they were good enough.

    Well, after enough rounds that fired on the second strike I realized they weren't seated fully and the first strike was pressing the primers deeper.

    Since I started hand priming, failure-to-fire is now a distant memory and my fingers can "feel" the primers seating just slightly below the case bottom.
     
  12. The Bushmaster

    The Bushmaster Member

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    MachIVshooter...measuring the primer depth will not insure that the primer is seated all the way and armed.
     
  13. PCCUSNRET

    PCCUSNRET Member

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    I never measured mine, I just seated them as deep as I could using a RCBS Hand Primer. I had never experienced any problem doing it this way until last week. I was priming some Remington 7mm mag brass using the recommended shellholder (#4) and noticed the primers were protruding just slightly above the bottom of the case. Since this was the first time priming 7mm magnum cases I figured they must be seated properly since I had sqeezed the priming tool handle as far as it would go. I decided to try a couple of the pieces of brass in the gun and found that the primers were scratched from hitting the bolt face or firing pin. Anyhow, I discovered the problem was there was too much play in the shellholder and I had to reseat a couple hundred primers with my press. I called RCBS and they said to return the shellholder to where I bought it and to try another number (#26 I believe).
     
  14. MachIVshooter

    MachIVshooter Member

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    I know. And I don't measure them. Just ram 'em home with the RCBS hand priming tool.
     
  15. Leaky Waders

    Leaky Waders Member

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    Primer seating depth is one of those measurements that confuse us new reloaders...you're trying to do everything 'right' and read the texts and after shooting your first batch and having a few misfires or rounds that needs struck you quickly learn that primer seating depth = all the way in.
     
  16. James2

    James2 Member

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    Hmmmm, a lot of to-do over nothing. Press them in until they hit bottom. Done.
     
  17. jcwit

    jcwit Member

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    Very simple to know if primer is deep enough, and if you don't trust the "feel" with your finger.

    1. Seat Primer
    2. Set shell casing on flat surface with primer down
    3. If shell casing rocks & rolls, primer is not deep enough

    There you go boys & girls.
     
  18. bds

    bds Member

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    Actually, this test won't help with some newer Speer/CCI cases as the center of the case bottom, where the primer pockets is located, is lower/deeper than the case bottom rim. I have intentionally seated primers "high" in these cases and although the primer sticks above the case bottom, they do not "rock and sway" when placed flat on the bench.

    Remember that a primer seated "flush" with the case bottom IS NOT seated all the way in. If you don't believe me, just check the primers on the new factory ammunition - you will find them all to be just slightly below the case base bottom.

    I loaded 1500 cases yesterday for a range practice/test load session for today and thought I compare the press priming vs hand priming. Even though I pressed "hard" on the ram lever on my Pro 1000 press to seat the primers, 2/3 of the primers came out about flush with the case bottom and 1/3 just barely below the case bottom. However, all the cases I hand primed resulted in primers seated below the case bottom. This is one of many reasons why I hand prime all of my pistol cases now - no more failure-to-fire.

    Some will undoubtedly argue that their flat/flush seated primers fire fine without any problems. I would agree IF your combination of soft brass/bronze cupped primers and hard hammer/striker spring provides enough force to ignite the primer that is not fully seated. But if you use harder nickel plated primer cup and have softer hammer/striker spring, first strike will only seat the primer deeper and not ignite it.

    For me, since I load for multiple pistols, I make it my standard practice to produce rounds that will ge "bang" no matter what pistol they are fired in. It is for this reason why all of my cases get full-length sized, minimally flared/taper crimped to fit the tightest chambers and primers seated below the case bottom.

    For you, if the flush seated primers fire fine in your pistols, great. If you have primers that fail to ignite on the first strike, seat them deeper. :D
     
  19. 918v

    918v Member

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    I hand seat my primers with a Hornady tool. I don't measure the seating depth. I feel the primer bottom out against the bottom of the primer pocket. That is the correct seating depth- when you feel the feet of the primer anvil bottom out and then just a bit more to preload the priming mix as BDS described above.
     
  20. Dave P

    Dave P Member

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    Some of you scoff at measuring the depth, but it is an important safety issue when shooting Garands and M14's and such, with floating firing pins.

    Having a recessed primer ( because you standardized each case with your deluxe pocket reamer tool) makes the round more resistant to a slam fire from the firing pin slamming into it when the bolt closes.

    I am not sure of the preferred depth, but mine measure about 8 mils below the head.
     
  21. The Bushmaster

    The Bushmaster Member

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  22. 918v

    918v Member

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    Can you explain how primer depth interacts with a floating firing pin?
     
  23. jcwit

    jcwit Member

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    Have yet to have a misfire caused by how I seat a primer flush or below flush. I've either been lucky for over 45 years or I have dern strong hammer striker springs. I don't even have problems with small rifle in small pistol applications.

    Then again maybe I haven't walked through the pasture long enough.
     
  24. mallc

    mallc Member

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    Hmmm...

    Apparently, this is another reloading issue which is far more complex than I understood. All this time I've just been seating to the bottom of the stroke; be it progressive press, or RCBS hand priming tool.

    I now realize how lucky I am that I've not been blown - and that I really must learn to worry more about such things!

    Scott ;)
     
  25. GW Staar

    GW Staar Member

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    You guys that are priming with hand primers may not need to think so much about primer depth, but those who do progressive reloading for gas operated semi-autos do.

    Slam fires, in such semi-autos, are usually primer-caused, in less-than-perfect reloads. They are either caused by high primers, or not fully seated primers. Then there are thin-cupped primers (like some Federals) that can and have caused slam fires, seated flush or even slightly recessed. That means that some assurance is necessary, that you can seat your primers correctly and progressively, for safe reloads.

    Head space concerns, when reloading for these rifles is equally critical, but that's another subject. See the Fulton Armory Url below.

    My RCBS Pro-2000 has a mechanical stop that is set to seat the primers at the same depth every time. But there's one small problem. The depth of the pocket can vary. That means that they could be "floating" (not bottomed), just right, or crushed. There's two ways to prevent such problems on an RCBS progressive. One way is to prime manually. The other, & the way I do it, is to use the primer pocket uniformer on the Trim Mate, so that every pocket I load is the same depth. Therefore, I find it useful while setting up, and testing the setup, to use the tail of my calipers to check primer depth.

    Floating firing pins really have caused problems with primers in gas guns. CCI even makes a special "military" primer to make sure the floating firing pins in military rifles don't make for a bad day at the range or on a hunt. They aren't absolutely necessary, but they probably are a safer choice for M1 Garrands and maybe even M1A's. Important reading from Speer on the subject


    And since I've talked about reloading for gas guns, I suggest those who haven't yet, read the following from Fulton Armory That website hides their internal pages, so once you get to the Fulton Armory site, go to their FAQ page, then to the "Reloading for Gas Guns" page.

    Not that I agree with Clint McKee that gas guns shouldn't be reloaded (he manufactures them you know, and what manufacturer condones putting reloads in their guns), but his points still provide the clues to why so many gas guns blow up with reloads, and shooters should learn from, or repeat the mistakes of others. I for one feel safer heeding the warnings.
     
    Last edited: Apr 24, 2010
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