Correct primer ignition is a key to consistent velocities and good accuracy, and maybe even survival! Let’s make sure the primer pops proper. Read how…

Glen Zediker

Last two times we’ve looked at the tools and process of seating primers and also the thing itself. This time let’s take it another step and perfect the important step of priming a centerfire case.

primer pocket uniforming
Very important step, in my mind, in the reloading process: uniforming primer pockets.


As gone on about in the first article, it’s very important to seat each and every primer flush to the bottom of the cartridge case priming pocket. Tool choice has a whopping lot to do with how well attaining that goal can be reached, and that’s because it is a “feel” operation.

However! Probably the biggest asset to correct primer seating is a primer pocket that’s correctly dimensioned and correctly finished. And this, in effect, removes some of the importance or contribution of the “feel” needed and that’s because when the primer stops it will stop flat and flush. If the pocket is what it should be.

With the exception of a very few (and expensive) cases, the primer flash hole and the primer pocket itself are punched, not drilled and milled. That’s done, of course, in the interest of efficiency in producing the case. That manufacturing process, though, hain’t perfect.

Cross-section a case head and you’ll see that the inside bottom of the pocket is a little bowl-shaped; the corners aren’t square, which means the bottom of the pocket isn’t flat all across. Since the bottom of a primer cup is indeed flat, it’s way on better if these surfaces are a match.

primer pocket uniforming

A “primer pocket uniformer” fixes this to the same level it would be had it been machined: it will be at “blueprint” specs. A uniforming tool also sets pocket depth and will correct a shallow pocket. And again, the flat primer cup mated with an equally flat primer pocket bottom results in a truly well-seated primer.

In my estimation, I think this is an even more important procedure or preparation step for those using any automated or semi-automated priming process, such as encountered on a progressive-style press than it is for “precision” handloaders. In short: the less feel in the tool that’s available to guide you to know the primer has seated completely is offset a whopping lot by the assurance that flat-to-flat flush contact results pretty much just from running the press handle fully.

primer pocket uniforming tool
Primer pocket uniforming is done fastest and easiest with a tool that chucks into a drill. There are many available, and I recommend getting a “fixed” depth design. One thing: unlike virtually all other case-preparation steps, pocket uniforming is usually best one on once-fired, not new, brass. That’s because the pockets can be a little difficult for the tool to enter when the pockets are at their smallest, which they will be as new.

It’s another step, though, that adds time and tedium to the reloading process. Add power and it’s a lot easier, and, for the majority, has only to be done once. True, after enough firings a pocket will get shallower, and it will also be getting larger in diameter. Usually the increased diameter outruns the loss of depth in signaling the end of case life.

I use mine in place of a primer pocket cleaning tool. There is zero harm in running a uniformer each use for reloading. Uniformers are available as fixed- and adjustable-depth. I generally recommend getting a fixed tool, and then trusting it. Setting depth on an adjustable model is tedious, and critical. Too deep can weaken the case.

uniformed pocket
Here’s a little (important) something that you might notice after uniforming primer pockets. The case on the right shows very clear primer anvil impressions, and that’s because this primer was seated fully flush into a uniformed pocket; the case on the left was not uniformed and likewise the primer was not fully seated flush (couldn’t be).

If you’re wanting to load once-fired mil-spec cases, or have to load once-fired mil-spec cases, then the original primer crimp must be removed. A primer crimp is small lip of brass that’s pinched into the primer edge during the primer seating process. It holds the primer in place against inertia-induced movement that might unseat it. Now, you never ever need to worry about crimping your own ammunition. All that matters to us is removing the excess brass residual from the original crimp. The most simple, and fastest, way is using a primer pocket swaging tool. These are either press-mounted or stand-alone stations. Just run it, run it out, and the pocket has been swaged to unimpeded roundness again. It is possible to use a uniformer to remove crimp, but it’s a tool for another job and, almost always, it’s best to use specific tools for specific jobs. It’s a difficult chore with a uniformer, and the uniformer also may not smooth the entryway adequately.

primer pocket swaging tools
If you need to remove the crimp from mil-spec cases, get a swager. It’s the best tool for the job. They’re easy to use, and, as with other such processes, has only to be done once for the life of that case. After swaging, by all means run a uniformer if wanted. Check out tools HERE

Overall, get a swager and keep it simple. They’re not expensive, they’re easy to use, and, as with other such processes, has only to be done once for the life of that case. After swaging, by all means run a uniformer if wanted.

Should primer pockets be cleaned? Why not… There is probably no influence on accuracy if the pocket is dirty or spotless, but, why not… Deprime prior to case cleaning to get that area treated. I preach heavily on the virtues of a stand-along decapping station to keep grit out of the sizing die. A primer pocket cleaner is fast and easy to use, but, as mentioned, I instead just run a uniforming tool in its place.

As said a few times in this series, the most important thing is to know that the primers (all of them) have seated to at least slightly below flush with the case base. Just seeing that does, in no way, mean each primer is seated to perfection. There are variances in (un-uniformed) primer pocket depths. At the least, one more time, uniformed pockets will or sure should take a big step toward providing more certainty.

A “high” primer, one that’s not seated fully to the bottom of its pocket, results in a “soft” strike from the firing pin, and that’s because some of the inertia/energy in the speeding pin is siphoned away because it first will fully seat the primer… However! There’s another, even more important reason all primers should be seated fully: When used with a rifle having a floating-style firing pin, which is an AR15, the normal and unavoidable inertia-induced firing pin movement upon bolt closing will result in the firing pin tip contacting the primer. It will bounce or tap off the primer. If the primer is sitting out farther, there’s a greater likelihood of setting off the cap. That’s called a “slam-fire” and its aftermath ranges from shaken nerves to shrapnel infestations about the facial area.

AR15 firing pin indentation
Yikes! Here’s a round chambered and then pulled from one of my AR15s. Floating firing pins can “tap” off a primer, it’s intertia-induced. A more sensitive primer, and it could have gone off. This is not “supposed” to happen via rifle design, but, well, here it is. Make double-dang sure all the primers are seated below flush with the case head! It’s a problem with any floating-pin equipped rifle: M1A, M1, AR10, AR15. Primer composition matters. In this case, its resistance to detonation, and it should influence decisions on primer brands.

See what’s available at Midsouth HERE

The information in this article is from Glen’s newest book, Top-Grade Ammo, available HERE at Midsouth. Also check HERE for more information about this and other publications from Zediker Publishing.

21 thoughts on “RELOADERS CORNER: Priming 3”

  1. Your first photo in “Primer 3” celebrates the bright shiny pocket bottom, missing metal from the bottom of the primer cup as essential to good priming. IMO, nothing could be further from the truth. Just brush the lead styphnate ash and burnt powder soot, out of the bottom of the pocket. That is all that is required. The primer cup elevates away from the bottom of the pocket when it first pressurizes during firing. The gas seal is on the circumference of the cup and the cylindrical surface of the pocket. How thin do you want your students to make the radially unsupported, pressure bulkhead membrane of the case, before firing that NATO pressure hot load? How much brass do you want to whittle off, to get that “bling” appearance of milled pocket bottom?

    1. It’s not for looks and you know it. The primer support area is consistent and only the process for creating the pocket is flawed. Uniforming with a precision tool keeps the design tolerance intact and produces a better ignition source.

      If you are not comfortable with that concept, then don’t do it.

      1. Not in my experience.

        And I am uncomfortable in teaching those new to the art of reloading that it is OK to mill out the bottom of the pocket, even and up to doing it every reload cycle. One side of the radially unsupported pressure bulkhead of the case is coincident with the primer cup bottom.

        Yes, the legs of the anvil need to contact the pocket bottom and press the legs up in the cup until flush with the cup rim.
        But, that will happen on a properly inserted primer regardless of pocket depth.

        When you mill out the bottom of the pocket, you are thinning the highly stressed bulkhead membrane of the high pressure plasma retaining end of the case.

        See Varmintal’s seminal work on case pressure, stresses and strains using non-linear code LS-DYNA.

      2. A proper fixed uniforming tool will not remove more metal if used as a cleaner to remove carbon. But it will dull it after time. I don’t do that and use a brush. Do pockets even need cleaned? I don’t know but I do it anyway. A tumbler will not clean unless you use the stainless pins but not me, I use walnut or corn cob media.
        A friend uses a collet to turn brass with a drill with steel wool. then inside too, then polishes cast with it so they are pretty. I don’t understand at all.

  2. The metal removed to uniform a pocket is so little as to be no consequence and will not weaken a case. Proper seating is the most important thing. As the anvil is pushed level to the cup the primer is where it should be. Never more pressure then that. By removing the rounded corners, feel is improved and a primer can be more flush. Even the use of the proper primer for the case capacity is important as some manuals call for a magnum primer when it is too much. 66 years with primers has shown a .44 magnum never needs a magnum primer with any powder, even 296. Nor does the .45 Colt.
    Next you must have a strong hammer or firing pin spring, never use reduced power springs. For accuracy I replace factory springs with over power. Every primer needs a certain force to get the best ignition.

    1. James, I will utterly disagree in regard to fired slow-burning, difficult-to-ignite ball powders in Magnum cases with std primers. Apparently, you’ve never shot in the cold. I’ve had several squibs in 44 and 357 cases using 296 and H110. They have all occurred at temperatures below 30 degrees F.

      1. Oh yes, down to -20° in Ohio.
        A squib can caused by a primer pushing the bullet out before ignition resulting in air space not wanted with a ball powder, slippery lube or lack of case tension. Near 40 years of the Fed 150 in the .44 has never failed me. Ball powder is not hard it light but you need it close to flame. 1000 tests with primers has shown a mag primer in a .44 will triple groups no matter the heat or cold.
        Loading the revolver is something I wish I could go all out for you here. I have shot groups to 3/4″ at 200 meters with a Ruger SBH. To load correct is easy but the net is full of false information. Ask and I will help. All I have figured out would use all the space here. Failures are not the powder, it is what you did.

      2. Again, James, no. It is common knowledge that ball powders, compressed under a bullet, require quite a bit of heat to get to ignite properly. Generations of shooters have found this to be the case, particularly when cold temps are involved. Any ole’ primer isn’t necessarily going to do it. Bullet manufacturers recommend magnum primers with certain powders. Powder manufacturers recommend hotter primers with certain powders. And you are telling me that you are correct, whereas I, and several generations of shooters, and powder and bullet manufacturers’s tests, are wrong? NO, James.

        And for your information, most of the squib occurrences I’ve seen or experienced have happened in lever guns, with only a couple in revolvers. What that tells me is that the platform is not the problem, but that the lack of a hot primer when using hard-to-ignite ball powders in compressed charges, even in heavily crimped brass (that’s all I use for straight-wall cases) need a hotter primer to ignite properly in below-freezing temps. Funny, this is just exactly what gun writers have found, and powder manufacturers, and bullet manufacturers….

      3. I have tested more then anyone and even tested the Fed 150 in the .475, .500 JRH and the .500 S&W with no ignition problems but large cases are more accurate with a magnum 155. All with 296. My start for the 155 is the .475.
        I have owned 8 or 9 .44’s since 1956 and my SBH has well over 89,000 shots with 296 in all weather conditions without a failure. I became so used to the .44 that if you bring loads for me to shoot I will tell you what primer you used. Got into many arguments of course, called fed once and the lady went back through records and told me there is no record on file of ever using a magnum primer in .44 factory loads. Call them, great people.
        296 is a great powder and needs little air space but there is no reason for a compressed load, over load but the powder is forgiving and will not spike. I load to accuracy and not velocity, even 1/2 gr can open groups. Why compress 296 or H110?
        The lever gun in .44 mag has the wrong twist of 1 in 38″ and the case is not able to reach velocity and spin.

    2. No, I disagree. In this same thread there is talk of misfires and the importance of keeping the primer cup below head face surface by a few thousandths but no more. This is to assure ample contact of the firing pin onto the primer cup top surface when firing.

      Oh, but we should mill out the bottom of the primer pocket to give it that “bling” appearance, and for good measure do it every reload cycle according to the article. That is utter BS.

      1. The uniform tool does not deepen pockets, just takes out rounded corners and flattens the surface. BR shooters do it and remove burrs at the flash hole.
        You will not ream the sides at all. I run revolver loads to near 60,000 psi and you will not shoot many of my loads without complaining. Not made for max velocity, just where accuracy is.
        Not the .44 of course but the big calibers in the BFR’s and Freedoms.
        You will not weaken a case with a uniforming tool.

  3. Priming 3
    I must agree with Glen and his write -up and Miner’s comments. I have been reloading for over 55 years and everything from .22 Hornets to .458 Win. Mags, and powders from Bullseye to H870. Have never had a misfire in temps from near Zero to over 100 Deg.. I use a uniformer to be certain the primer pocket is clean and uniform depth around the perimeter of the pocket to insure primers are sub-flush with the head. Insufficient striker force is usually the culprit in misfires /poor ignition. Take a look at firing pin protrusion on a Mauser ’98 bolt some time.

  4. Total waste of time for loading handgun brass if you use a hand held tool to prime your cases. I personally don’t trust any tube fed priming system (I have grown attached to my fingers). And if you tumble your cases with fine enough corn cob media (read: 20/40) it will clean the primer pockets of your deprimed brass.

    1. I have primed every way you can and still prefer the lee hand tool, been using it since it came out. I also like the Bonanza tool. Many presses have to much pressure and feel is not there. There is false info about using Fed primers in the Lee, they are not prone to go off and have been all I have used for more years then I admit. In 66 years I have never had a primer go off by accident but a friend did, he lost one on the bench and soldered water pipe in his vise, found the primer with the torch. No harm done.
      When a primer does not do what I want and needs changed I have removed many live primers. I do not use them over since a fracture in the compound can change accuracy.

  5. Let me talk about the .454 and the SR mag primer with 296 or H110. Working with them for others has shown failures to ignite with starting loads no matter the primer used. Brass rod and hammer in my shooting bag. Funny to see the bullet up the bore with all the powder packed behind it. Primer pressure with loss of fire. Only at max did the guns work.
    I cut cases for the LP mag primer and all loads fired, even made it more accurate, then found cutting down .460 brass solved it all.
    Going on to the .45 ACP revolver, new S&W that was a shotgun. No load worked. I sat at the bench with my friend, said “too much primer.” I made bushings to take the brass to a SP primer. Came in very accurate since the primer was not moving the bullet. He bought 1000 SP cases, Speer. They even shoot better in his 1911.
    Yes a primer will move the bullet and the powder. There is a difference between pressure and heat.
    I believe nothing in print or the net without many tests.
    Manuals are wrong too, notice a Mag primer is listed for Bullseye, Red Dot, Green Dot and up. Did you ever wonder? Is it the stamp on the case head?

  6. James W Miner,

    I would very much like to converse with you as you have a considerable amount of knowledge and many many years of experience reloading ammo. Please feel free to email me and I will contact you. I have tremendous respect for your common sense, obvious experience and “old school” abilities. Best wishes, Dale

  7. I am actually enjoying this conversation. In my S & W 6″ 629 .44 mag I have been using H110 and 2400 with magnum primers and 240 grain bullets. I use both lead and jacketed. I have been happy with these loads but it seems like you guys experiment a lot more than I do. I live in Kodiak, AK and mostly just carry it around when I go fishing and stuff. So just for bears. What do you think would be the best load?

    1. The S&W is one of the finest revolvers made. I advocate heavy bullets but not in the S&W since you might have recoil inertia issues. We found a 265 gr cast like the RD really shoots good without harm to gun parts. 22 gr of 296 and YES, I still use a Fed 150 primer. I don’t think any bear would stop the load.

  8. The LR and LP have different heights so a LP will be deeper but a proper gun, rifle or any will fire both. I use LP mags in the 45-70 rifle too.
    It is testing to see what works best. I have no fear of a LP with pressures until so high a LR is needed.

  9. The .500 S&W came out for a LP mag and it worked fine but then they changed to a LR for some reason. Guys did not understand so loaded LR in LP pockets, does not work and a slam fire can be had, The head stamp was changed to show LR. But a LP mag works fine in a LR case. Not the other way. Then some said crush the LR primer in more so it is level—WELL???.
    I run out of expletives.

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