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Thread: Primer Seating Depth ?

  1. #1
    Boolit Mold 10mm Witness's Avatar
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    Primer Seating Depth ?

    I have been reloading for 10 years of and on when I need. Over time I have amassed a few rounds that have not fired. I have tried to fire them twice. The firing pin has put a nice dent in the primer. I cant say I have a bad batch of primers as it has happened when I use different manufacturers. I think I am causing it by the seating depth. I may not be verifying the depth is not consistent. As any Reloader knows the primer consists of a cup, flammable material and a 3 pronged metal piece. My question is when the primer is seated does the cups lip surface touch the bottom of the casings primer pocket or does the edges of 3 pronged metal piece? I tend to believe the 3 pronged metal piece does so it is stationary. This way when the pin strikes the face of the cup the cups inner surface forms a bulge that smashes the flammable material between it and the 3 pronged metal piece. If this is the case then should I set the cup depth on the casing to the thickness between the primer cup face to the edges of the 3 pronged metal piece?
    Jim Ceglinski
    Southfield, Mi. 48075

  2. #2
    Boolit Master
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    I have a Sinclair primer pocket uniformer that allows me to ream the primer pocket dead flat and to a set depth as prescribed by them. It is adjustable by a set screw and can be changed as needed. I set it to the correct depth many years ago and have not touched it since. I do not remember what the depth was but what I remember about setting it was that I measure the primer I nearly always use(Federal) and set it for those and I have not had a primer fail to fire since. I do it both for new or fired brass when I load them the first time. It is not necessary after that. My primers when seated by hand with a Lee or RCBS hand priming tool seat just barely lower than the case base head. And by using a hand priming tool I can feel them when they seat flat and solid against the bottom of the primer pocket. I also rotate them 1/2 way around and set a second time just to make sure they are seated flat. I do not crimp hard enough to crush them just good solid contact. I do this on both rifle and pistol cases by using separate primer pocket tools (one for pistol depth and one for rifle depth). I haven't had a failure to fire since I started using this system many years ago. my experience anyway, james

  3. #3
    Boolit Master
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    what said he ^ said.

  4. #4
    Boolit Buddy gumbo333's Avatar
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    10mm it is much easier to seat primers with even a cheap Lee hand primer than on a press. But even with seating with a press I think you have to really seat with a lot of force to seat so deeply that you wouldn't feel it sort of crushing. But I haven't seated on with my press in over 40 years. My thought is that the primer(s) somehow became contaminated. Do you pick them up with your fingers? I've used Win, Rem, Fed and CCI primers over many, many years. Maybe once or twice a year I experience a dud when shooting my paper. I always figure I got it contaminated some how. But it could be something done when it was made like not enough compound or no anvil, etc. Like most I don't check them that closely when I load my hand primer.
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  5. #5
    Boolit Grand Master

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    Actually the anvil is floating when in the box and seating "arms it. The cup when seated pushes in to the primer pocket and the anvil seats inside the cup to rest on the priming pellet. This happens with little notice by hand loaders. What is probably happening is you dont always get the primer armed and seating the cup the last little bit weakens the strikers blow and breaks the pellet up.

    Ideally primers are seated by feel just bottoming in the pocket snugly. This arms them and dosnt damage the pellet. Do to variations in primer pockets depth and squareness actual depth below the head will vary a little. I have seen pockets vary in depth square and a radius in the corner ( You cant form a perfectly square corner with a punch).

    Uniforming pockets has several benefits when done properly. 1) it cuts the pockets to a much closer depth to each other meaning uniform seating. 2) It squares the bottom of the pocket and makes it flat meaning the legs of the anvil bear evenly and solider. 3) it removes the radius in the corner allowing the cup and anvil to seat flatter with full bearing on the surfaces. Only take what you need to clean up the pockets to much and primers are to deep. It usually only takes .001-.002 to clean them up but on that small dia thats a lot.

    You can see the improvements in uniforming by watching chrono reading Load some standard then uniform them and chrono them extreme spreads will be lower as will standard deviation

  6. #6
    Boolit Master


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    In my experience, the Federal primers are the easiest to get ignition with. They seem to have a softer cup material and they are what I used for CAS as my "tuned" revolvers and 1873 had a light hammer strikes. I could not get reliable performance with Winchesters....but the Winchesters worked in my 9mm loads and other .38/.357 weapons.

    The advice from TNsailorman is a excellent if you wish to invest the time to "do it right". I have never cleaned or prepped a primer pocket for pistol loads as I reload on a progressive and productivity is important to me. Plus, I have very few FTF's, so there is little incentive to fix a problem I do not have.

    In your case, I would inspect the seating depth of your loads to determine if you have a seating depth issue. I do not measure it, but run my finger over the primer to insure it is just a hair (special engineering measurement) below the case head. The bulk of my pistol reloads are produced on a Dillon 1050 that primes on the downstroke...that gives more consistency than other presses (the Star does that as well). Primer depth is adjustable and once set, I have never had to tweak it.

    But I have reloaded on the 550 and not had any issues either so you may have other issues.

    BTW, if "uniform" primer pockets were necessary, factory ammunition would be unreliable so think about that. I have .38 cases that have been reloaded 30+ times and have never prepped a primer pocket (uniformed it or cleaned). Maybe I am lucky.

    It will be interesting to see what others do.
    Don Verna

    NRA Endowment Member

  7. #7
    Boolit Buddy
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    While I don’t have decades of experience. The few thousand primers I have seated on my Lee Classic Cast have all been touched by my hands. They all went off. It seems that there are two camps with primer handling the “rubber glove and tweezer” camp and then the rest of us. I’ve read many threads about primer handling, and have come to the conclusion that clean dry hands won’t contaminate a primer.

    I do however have a cheap imported aluminum frame revolver that misfires (that I purchased when I was young). It has a light double action hammer strike. It is the only gun that I get misfires with. Both factory and reloads. But what do you expect for seventy-five bucks.

    So, at least in my limited experience, a primer not going off is related to a mechanical problem with my firearm.

    JM

  8. #8
    Boolit Master
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    Quote Originally Posted by JM7.7x58 View Post
    While I don’t have decades of experience. The few thousand primers I have seated on my Lee Classic Cast have all been touched by my hands. They all went off. It seems that there are two camps with primer handling the “rubber glove and tweezer” camp and then the rest of us. I’ve read many threads about primer handling, and have come to the conclusion that clean dry hands won’t contaminate a primer.

    I do however have a cheap imported aluminum frame revolver that misfires (that I purchased when I was young). It has a light double action hammer strike. It is the only gun that I get misfires with. Both factory and reloads. But what do you expect for seventy-five bucks.

    So, at least in my limited experience, a primer not going off is related to a mechanical problem with my firearm.

    JM
    I'm in the Clean Dry Hands camp, never had a primer fail. Rubber gloves are too flimsy or don't fit me. Tweezers aren't worth my time except for things that are too small to pick up.
    Too bad your revolver isn't worth more, then you'd be able to justify new springs (if they could be found). Maybe give the old ones a careful stretch.
    Warning: I know Judo. If you force me to prove it I'll shoot you.

  9. #9
    Boolit Buddy
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    Quote Originally Posted by JSnover View Post
    I'm in the Clean Dry Hands camp, never had a primer fail. Rubber gloves are too flimsy or don't fit me. Tweezers aren't worth my time except for things that are too small to pick up.
    Too bad your revolver isn't worth more, then you'd be able to justify new springs (if they could be found). Maybe give the old ones a careful stretch.
    That old revolver pretty much lives in the back of the safe. I have a nice Security Six that replaced it 15 years ago. I think that I will try to stretch that spring a little. Thanks for the hint.

    JM

  10. #10
    Boolit Master
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    I use the sinclair primer pocket uniformer in the chuck of my mini lathe and push the brass on as far as it will cut. It is a solid carbide cutter with no adjustment. On my Dillon 550b I don't touch the primers by hand but on my Lyman AA and my coax I hand set them. I always seat them on the press firmly. I don't use the uniformer on pistol brass. Years ago I had about a dozen primers fail to fire from a batch of 50 rounds and I think it was from loading cases that hadn't dried completely after cleaning. Since then I haven't had any problems other than a tarus 32S&W L that has a light hammer strike. Federal primers fixed that.

    My guess is that you are not seating them firmly enough to get the cup to seat against the bottom of the pocket. I have mashed some pretty hard over the years and have not had one fail to fire from that.

  11. #11
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    If you look at a new primer from the side, you'll notice that the legs of the anvil are set slightly above the lip of the primer cup. This is done by the factory on purpose. When a primer is properly seated, it will be all the way to the bottom of the primer pocket, which means the lip of the primer cup will be resting firmly against the bottom of the pocket. This forces the anvil legs to be even with the edge of the primer cup, and is calculated to be the proper distance of the top of the anvil in relation to the primer cup, with the priming pellet between the two. This normally results in primers being seated roughly .004" +/- below flush with the base of the case.

    When primers are seated properly, they go off every time. Primers are also hard to kill. I've sprayed seated primers with penetrating oil from inside the case and let them set for a couple of days, and in most cases they will still fire. The priming compound is made under water, and is dried after being placed in the primer pocket, so water isn't going to kill a primer, unless it's still wet. After it dries, it's a primer again. Priming compound is an actual explosive, by the way. Lead Styphnate, Diazodinitrophenol (DDNP) and the newer Federal Catalyst priming compounds are all classed as explosives.

    I've loaded well over 850,000 rounds of ammunition in my 57 years of reloading, and I've handled just about every one of those primers. I've yet to contaminate one with my hands so it wouldn't fire when hit with a properly sprung firing pin. With that said, I'd never tell anyone how they should do it in their shop, so if using gloves and tweezers works for you, then by all means use what's best for you.

    Hope this helps.

    Fred
    After a shooting spree, they always want to take the guns away from the people who didn't do it. - William S. Burroughs.

  12. #12
    Boolit Grand Master Outpost75's Avatar
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    When cases are repeatedly reloaded and if you don't clean primer pockets to bare metal, thus seating the primer in a dirty primer pocket, the accumulated residue cushions the striker blow and may also prevent the primer anvil legs from seating properly. I have also found that the cheap zinc die-cast linkages in the Lee priming tools wear with extended use, and prevent a full stroke of the priming punch. I use the RCBS priming tool.
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  13. #13
    Boolit Master
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    I load pistol on a 550 and for rifle I use a RCBS bench priming tool and don't clean primer pockets other than wet tumbling deprimed brass.
    The only way I have found to kill a primer is to go out side with hearing protection, eye protection and a 4 lb hammer on a hard surface like concert.

  14. #14
    Boolit Master


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    Quote Originally Posted by Outpost75 View Post
    When cases are repeatedly reloaded and if you don't clean primer pockets to bare metal, thus seating the primer in a dirty primer pocket, the accumulated residue cushions the striker blow and may also prevent the primer anvil legs from seating properly. I have also found that the cheap zinc die-cast linkages in the Lee priming tools wear with extended use, and prevent a full stroke of the priming punch. I use the RCBS priming tool.
    The only primer pockets I clean are on rifle cases and the crud does not seem soft enough to act as a cushion...but I will need to check that now that you brought it up. Wouldn't build up improve the seating the anvil legs? If the ideal seating depth is -.004", and there is a .004" build up in the pocket, even a flush primer will set the anvil adequately...assuming the build up is not soft.

    Maybe I am not seeing any problems because most of my pistol ammo is/was loaded on a Star or Dillon 1050 where primers are not seated by feel but with a positive mechanical stop. It is possible to have a primer not seated fully with other loaders and that can cause a misfire.

    I load 9mm about five or six times as it is so cheap I am not anal about chasing it and getting my brass back. So not a lot of build up likely occurs. The .38's are different...I load them until they split. None of the pistol brass is lost and maybe one in 10 from the lever actions is lost. Those .38 cases must be horrible but still work. The only cleaning I so is with a vibratory tumbler and cases are not deprimed before cleaning. Maybe the build up gets so compressed by the Star and 1050 "positive" priming system that it masks the problem with buildup?
    Don Verna

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  15. #15
    Boolit Grand Master

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    Seat primers until they bottom out in the pocket .
    The anvil legs must rest on the primer pocket bottom to ignite .

    Seating them anywhere other than all the way in and bottomed out will invite the dreaded "light strike" , "hard primer cup " and "defective primers" that so many try to pass the blame on...
    the real fact is that they didn't seat the primers properly and they don't wont to admit it .
    Gary
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  16. #16
    Boolit Master
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    I clean the primer pockets when loading the case for Schuetzen... the same single case over and over at the bench during a match. This is about the only time my primer pockets get cleaned except when I tumble deprimed cases for pistol ammo. The largest percentage of my 32s (of all lengths) get hand primed, usually with an old 1st Gen Lee hand tool with screw in shell holders or some other simple, one-at-time hand tool. I like to be able to feel the primer seat to a consistent degree this way... which I don’t get with a press. In fact, the biggest problem I’ve experienced of late with my Dillon 550 is irregular primer seating as the operation of it has gotten generally bumpy due to its pure filthy condition.

    A long treatise, I realize, but to the OP’s question, I like to hand prime whenever possible to feel the primers go in the same each time... or I know something is wrong and that I need to stop and fix it.

    Froggie
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  17. #17
    Boolit Master 44magLeo's Avatar
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    I'm in the like to feel them seat camp. Even if your primer pockets are not all the same depth the primers are all seated so the anvil and cup are both firmly in contact with the bottom of the pocket.
    I do have a Sinclair Primer Pocket Uniformer. I bought it because I have some Sellier & Bellot brass in 7 mm Mauser and 7.62x54R That have shallow pockets.
    I can't get primers to seat flush, let alone recessed without using a lot of force. I don't like that. The uniformer gave me pockets deep enough.
    Some of the 7.62x54R Winchester brass I've got is shallow too.
    The uniformer make a good primer pocket cleaner too.
    If you use a uniformer then I think using a tool that has an adjustable stop when set right will give you primers seated to a consistent depth in firm contact with the bottom of pocket.
    Leo

  18. #18
    Boolit Master
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    In my experience, all of the primer carbon buildup has been thin and brittle, mine doesn't build up on me. Seems seating and firing each new primer breaks up and blows away any previous carbon residue.

  19. #19
    Boolit Grand Master

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    Couple of things. Yes, what has been said about American primers above is valid. Russian primers are not made that way. Their anvil is already seated and you have to be sure you fully seat Wolf and Tula primers.

    As stated, S&B brass has tight and small primer pockets. I'd bet, but don't know, that given the limits of the primer size, S&B primers probably run a little small and Tula a little large.
    Wayne the Shrink

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  20. #20
    Boolit Buddy
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    OP, you did pull the boolits on those rounds and see if you have a powder charge, right? Will the primer always push the bullet out of the case??? Never have tried it.
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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
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LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
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