Properly seating primers

[LiveLife]

There have been several threads on the virtues of properly seating primers (high, flush and below flush), to clean or not to clean primer pockets and hand priming vs press priming.

The Rifleman's Journal posted an article that addressed the priming issue and thought I shared it here. I realize that The Rifleman's Journal is a website focused on bench rest rifle reloading, but contains many reloading practices that are applicable for the rest of us. BTW, I deprime and hand prime my "match quality" cases separate from the progressive press loading - I do inspect the primer pockets and only clean pockets that I consider really dirty/cruddy. Here's a sample of my "deep seated" PMC primers in 40S&W cases.

Primers: Seating Pressure and Pre-Compression

I recently received the following note from a friend overseas. Since the question and answer have broad applicability, I'll put them here for future reference. I'll try to take and post some pictures for this in the next week or so, but it wasn't really something I had planned and I'll have to scrounge up a camera with macro capability from a friend so it might take a while.

Hello German,
I have enjoyed reading a few of your posts and articles about primers among other things. I read a post recently were someone has been seating their primers way too hard and after some measurements, it seems my big clumsy fists have been squeezing the primers a bit too hard as well, giving about .008" crush at least. On the rare occassion I have been able to test over a chrono, I had higher than expected ES, so I am thinking it could have been the primers jammed in way too hard?

I mainly use the Russian SRM and LR primers in my 6x47 Lapua and my .284. What sort of crush should we be looking for with these primers?

Thanks for any help, from Rod D.


Hello Rod,
Primers have a definite "sweet spot" in terms of seating pressure and pre-compression of the pellet. These days the manufacturers give out essentially no technical information on the properties of their primers, we're all taken to be semi-useful fools, I suppose. However, at one time, Federal used to recommend a "light pre-compression" now that's a pretty vague statement, but better than silence.

Creighton Audette tried to get some numbers from Federal and got nothing more from them. He then designed what is now sold as the K&M seating tool that allows you to measure how much pre-compression (crush) you are applying to the primer (K&M also makes a version without the gauge). Of course, the system depends on all primer pockets being uniformed for depth. After a great deal of experimentation with pre-compression and related accuracy testing, Creighton determined that there was no specific number, but you could definitely do too much or too little. Very ironic, a light pre-compression indeed turned out to be best... whatever that means. No one was better at this sort of testing than Creighton, by the way. I'm as chagrined at the non-numberical result as he was but not knocking his work in any way.

I use the Sinclair tool which is another version of the Audette design, although without the crush measuring ability. Both the Sinclair and the K&M give the best feel for what's happening as the primer seats of all the tools I've tried.

In my own testing, I have found that the best method is to clean the primer pocket (I don't uniform them) then, seat the primer until you feel it just touch, then apply a bit more pressure (not a lot) until you feel a second level of resistance just starting.

Photo from the Remington website shows how the anvil will pre-compress the pellet on seating (see article link for photo).

If you examine some new primers you'll see that the legs of the anvil stick out past the bottom of the cup. When the legs hit the bottom of the primer pocket you feel that first resistance. As you continue to apply pressure you bring the cup over the legs and then the second level of resistance begins as the center of the anvil begins to compress the pellet. Stop!

The primer pellet is very small, it typically weighs 0.5 gr. for a large rifle primer and it can be cracked through the application of too much seating pressure. However, it needs a tiny bit of pressure as the tip of the anvil should be in contact with it when the firing pin hits - it shouldn't have to move at the firing pin's impact to make contact with the anvil. If it has to move, or if it has been cracked, SD will increase.

To continue a bit with the unfortunately non-numerical approach, if the primer loses its edge radius on seating and looks somewhat concave, that's way too much pressure. A bit of flattening is normal and correct, but like Goldilocks testing the bears' mattresses, there's too soft, too firm and just right.

A worthwhile test might be to try chronographing three sets of loads, one in which you stop as soon as you get initial resistance (legs at the pocket bottom) one where you crush mightily, and one where you add a slight pre-compression as described above. The Goldilocks test so to speak. I would be very interested to hear your results and will do the same test myself next time I chronograph something.

 

[LiveLife]

I decided to add the primer on primer that's posted on Co-Ax website that I have used in the past to illustrate the proper seating depth of primers.

High primer - The middle drawing shows a primer that is seated too high and the primer cup has not been pushed enough into the primer pocket. Such high primer is the usual cause of misfires that will fire on the second strike as the first strike will push the primer cup further down only, which then sets the anvil to fire on the second strike.

Slightly below flush - The bottom drawing shows a properly seated primer that has the anvil against the priming compound and the top of the primer cup is below flush. Primer cup top is still rounded.

Crushed primer - The top drawing shows a primer that is seated all the way to the bottom with the anvil deeply cutting into the priming compound. The primer cup is flattened.

A Primer On Primer Seating

The following three drawings illustrate the critical nature of accurate primer seating.

Primer SeatingIllus. 1: IMPROPERLY SEATED - This primer is improperly seated, preventing the cups of the primers from resting solidly on the bottom of the primer. Some primer cups measure .120” in height, and if seated with crowns more than .004” below the case head, the anvil would be forced through the crown, rendering the primer useless.

Illus. 2: IMPROPERLY SEATED - This primer is improperly seated too high. A high primer is erratic in performance. It is also dangerous and could explode in the chamber of a rifle when the breech block closes on it before it is locked.

Illus. 3: PROPERLY SEATED - This primer is properly seated, exactly as it would be with our Co-Ax® Reloading Press. The crown is .004” below the surface of the case head; the anvils are on the bottom of the primer well; and the primer mix is properly stressed by the anvil for sensitivity. It is also much safer than either of the two seated primers shown above.

 

[armoredman]

The problem I have is Remington 9 1/2s in 7.62x39mm cases, as they will not seat below flush without a little extra pressure. They always have a slightly flattened look to them when they are in. I have cleaned every primer pocket, and no matter the brand of brass, this is always the result. They also always function. So am I doing it wrong?

 

[LiveLife]

They always have a slightly flattened look to them when they are in. I have cleaned every primer pocket, and no matter the brand of brass, this is always the result. They also always function. So am I doing it wrong?

It may be the case of softer primer cup. The PMC bronze/brass primer is much softer than Winchester bronze/brass primer cup and if I wanted to, I can easily push the Auto Prime lever all the way down to completely flatten the cup. As indicated in blue of the article, I normally stop when I feel the second resistance. As long as they function, I think having the primer cup below flush is more important in semi-auto rifles with floating firing pin than flattened primer cups to reduce slam fires.

Have you tried different primers?

 

[armoredman]

Yes, CCIs, and they seat easier, but were VERY hard to locate some time ago, so I have a lot of Remington primers instead.

 

[LiveLife]

So you didn't have the same seating problem with CCI?

Maybe you can swap your Remington primers for other primers in the Buy, Sell and Trade: Reloading Components and Gear section?

 

[cheygriz]

Remington 9 1/2 primers have slightly harder, slightly thicker cups, since they are manufactured to meet Milspec, and used in Remingtron military ammunition. (Remington 7 1/2 have the same fearures in small rifle primers)

A slight amount of flattening is fine as long as they function 100 percent.

Have you had any issues with them in anything other than 7.62X54R?

BTW, what brass are you using?

There are numerous variables involved.

 

[armoredman]

Mostly Winchester, being the cheapest to get, and it's 7.62x39mm, not 7.62x54R - never had any issues with those when I was loading that caliber. They always work, so I figured I wasn't doing any real damage, and I try not to mash them "too much."

 

[GLOOB]

I've never experienced a primer seated too deep. I get the occasional odd head stamp that doesn't take the primer, correctly. I think it has a crimped pocket. The primer ends up looking like a flowed primer, once it's stuffed in. The cup diameter actually expands at the top. Even these have gone bang. I guess it's a matter of time, but until I experience one, I'll err on the deep side.

 

[magnum338]

I'm a new member of this group but have been a handloader since 1954. I think there's another aspect of this subject that I want to mention, for what it's worth.

The anvils in Remington primers are seated flush with the primer cup "mouth." This requires a primer pocket with sharply defined corners, where the primer pocket side meets the web, for the anvil to bottom out on the web as it should. Remington cases (which I generally prefer) have that sharp corner, while Winchester cases are somewhat rounded. Therefore, Remington primers do not install below flush in Winchester cases because they meet that corner radius, and can't be pushed further, while Winchester primers, which have the anvil protruding slightly above the cup mouth, can seat deeply enough.

I'm sure this is true in other combinations, and in some that are not.

 

[Walkalong]

It is actually hard to "crush" a primer to the point it won't work. It is quite easy, however, to seat one too shallow and cause a misfire.

On another note, welcome to the forum magnum338

 

[Waywatcher]

My experience mirrors Walkalong's.

I accidently crushed the living heck out of one primer in a .38 special, seating it way too deep. I could make out the 'silhouette' of the point of the anvil through the primer cup!

Fired fine!

Haven't seated one too shallow yet.

 

[GLOOB]

I guess it's a matter of time, but until I experience one, I'll err on the deep side.

... and that time has come.

I found out the hard way that it's indeed possible to seat a primer too deep, if you shoot a Glock 9mm - which has the trifecta of loose extractor, short brass, and short firing pin. And of course, there's no way to fix a deep primer. So now I have several boxes of ammo that are questionable.

 

[LiveLife]

GLOOB, consider one more thing.

If your Glock has a lot of rounds shot through, it may have hard packed fouling buildup at the bottom of the striker tube, right behind the breech wall keeping the striker from making deep enough indent on the primer cup.

When I see lighter primer strike, I disassemble the slide and inspect the bottom of the striker tube. It's hard to see, because the hard packed fouling is black, the same color of the slide, but I plug the striker hole and soak the tube with Hoppes #9 20-30 minutes and scrape the hard packed fouling out with a small flat screwdriver.

Once the hard packed fouling is removed, no more light primer strike.

 

[243winxb]

Crimped Primer Pockets.

The crimped in primer seems to have caused the problem in this photo. If the crimp has not been removed fully or a burr was let in the pocket, primers may not seat fully 100% of the time. Swaging the primer pockets would have worked better here. IMO. http://www.thehighroad.org/showthread.php?p=7234618#post7234618

 

[GLOOB]

BDS, i'll be sure to check next time I breakdown that gun. It's definitely seen its share of rounds downrange, but I actually don't shoot that one much. My G27 gets most of the range time, these days.

Even if it IS dirty, I would still rather have ammo that will go bang with a crudded up Glock. So nowadays, I'm much more careful about stopping when I feel the second resistance. Just a light squeeze after they bottom out. Then I take care to touch up any primers that are proud. They're easy to spot when I put them on a loading block.

I also touched up the face of my priming arm, concaving it a little and taking some off one side. It was pushing one side of the primer deeper/flatter than the other. Now I get a fairly symmetrical, rounded crush on the primers that don't want to get flush without a little encouragement. This is a concern with these Tulammo primers, which are just a hair taller than CCI and a bit softer.

 

[LiveLife]

I would still rather have ammo that will go bang with a crudded up Glock. So nowadays

Actually, it should be, "I rather have a gun that will go bang with cruddy ammo"

Once I got the first Glock striker tube cleaned out, the primer indent was much deeper. When I showed the indent to Glock shooters at the next match, everyone commented they never checked the striker tube and their primer indent was shallower in comparison (and some have experienced FTF with light primer strikes). Needless to say, everyone had their striker tube cleaned out by the following match. No more light strikes/FTF were experienced by their Glocks thereafter. Now, when I do my annual Glock cleaning, I always check/clean out the striker tube bottom.

Update: Went through my bucket of range brass and found these. If your Glock primer cup strike looks like the top, you probably need to clean your striker tube bottom. If your primer cup strike looks like the bottom, you are GTG.

 

[Lunie]

Hmmm...

I prime on my press (Rock Chucker IV).

I do a 100% check to make sure all are seated flush or below.



Lately, I've noticed that most of my primers are rather flat, with a good chuck of the radius gone. I seat to the first level of resistance, then try to give a firm, consistent push on the lever to fully seat. A few end up being below flush, but are still a bit more rounded looking.

Sooo.... Am I seating most of these too hard/deep?

Knock on wood, I haven't had any misfires, hangfires, or anything noticeable out of the ordinary.

Planning to buy a hand priming tool soon, that may help keep me from overdoing it quite so much in the future.

 

[GLOOB]

Lunie,

From reading posts about the dangers of seating too shallow, and the relative non-issue of seating too deeply, I thought for pistol, the deeper the better. I figured the benchrest shooters could worry about perfect tension. I was only concerned that all my ammo worked. I seated my primers on a ram, exactly the way you did. I felt for when the primer got started in the hole, then just pressed it in and gave it a good squeeze.

After reading the info BDS posted above, in hindsight, I crushed every single primer I've ever seated up til my recent discovery. And until I started using Tulammo primers in a Glock, I never had a light strike. On measuring those dud primers, they were, indeed, as deep or deeper than any of the other primers on the rest of my ammo. I am measuring 0.011" deep around the centers. Since they are slightly taller and softer, I was crushing them a bit more than usual, to ensure that all were below flush. It also didn't help that I was coming off using CCI 400 rifle primers, which are a tad harder.

Now, it's dang hard for me to measure the length that the Glock striker protrudes from the breechface. But by eyeballing and measuring various shims, I am estimating around 0.050" to the tip. If the striker needs to indent, say 0.025" deep to reliably light the primer (just a total guess), then that would still ordinarily be fine. But the extractor on a Glock 9mm leaves some free space. And since most brass is well short of the chamber length of a Glock, the brass is basically spacing off the extractor. So add that slop in, and tada. My Glock 19 appears to have light strikes at primer depth of around 0.011" (which is way past the recommended 0.004" depth). It is no surprise to me that my G19 had these failures, and not my G27 with conversion barrel, because the 40SW extractor fits tighter! Of course this depends on primer sensitivity and the thickness of the rim on the brass, as well. But I'd say it's a pretty good guesstimate. Of course, the other thing is that I could have crushed the primer pellets. Perhaps those rounds won't fire, even in one of my other guns. I'll have to seat the bullets deeper to fit them in my other 9, but will definitely post the results if I ever get around to it and they don't light off.

Striker-fired guns generally NEED to have shorter firing pins, because of the mass of the striker. It can't retract as fast as a lighter firing pin. Thus, the external hammer fans can chalk this up as a con for the striker-fired mechanism.

To be clear, I just checked the striker channel to make sure it wasn't dirty. I couldn't leave well enough alone, so I actually spent the last 30 minutes making a custom scraper/jag for my Glock striker channels from a nail. There wasn't excessive carbon down there. I could see silver metal from the start, with just a spattering of dark spots. But it's now cleaner than ever.

I am sticking with the ram. I can easily feel for the second resistance, and my priming depth is very consistent. Last time I primed brass, I was a bit concerned because there were quite a few that were slightly proud. But then I noticed they were all the same headstamp. And ALL of that headstamp were protruding just slightly, using these taller Tula primers. So my seating was very consistent. I just gave those primers a bit of crush, and they all worked.

So, until i have a light strike on a primer that is seated too shallow, I'm now going to do what seems to be the concensus. Feel for the second resistance, and give a slight bit more pressure. If it's not flush, yet, crush it a little bit more until it is. I'm not shooting for below flush, anymore, unless that's where the anvil happens to seat. Bonus: my ammo now looks much more like factory, and I presume there will be less chance of peening caused by primers striking the breechface.

If your Glock primer cup strike looks like the top, you probably need to clean your striker tube bottom. If your primer cup strike looks like the bottom, you are GTG.

BDS, the striker marks on my fired brass are great. Very deep. Some actually have a bit of a burr on them where the striker isn't retracting fast enough. I have always routinely inspected and cleaned my striker channels, at least once a year.

 

[Walkalong]

I figured the benchrest shooters could worry about perfect tension. I was only concerned that all my ammo worked.

When a group of us where talking about priming one day, Allen Hall told us as long as the primer went bang, you did not have a problem.

Function first in pistol ammo.

 

[gamestalker]

Despite the fact that my single stage presses have the priming rod on them, I use an RCBS priming die on my single stage press. I adjust the die to set the primer in just below the surface, and prime without further thought. Too deep and not deep enough can cause mis-fires. But in this respect, it's not rocket science or I would have had some problems by now. I've been loading for almost 30 yrs. and as well have loaded 10s of thousands without one single mis-fire to date.

 

[Bmac1949]

After reading this post I loaded some .270 rounds (Win LRP) and paid close attention to the feel of the press and after the primers sliped into the socket I just nugged the lever just a tad more and then made sure the primer was recessed. I liked what I saw. There was no mark or dimple on the primer like I had been getting. It's actually a light touch to get them in there right. So bottom line I can prime with confidence now. I'm still in the steep part of the learning curve on reloading but ain't it fun to figure this stuff out?

 

[gamestalker]

Walkalong is absolutely correct. I've have yet to crush a primer, and I somtimes really test their limits. Using a priming die as I do, and not sorting my brass according to head stamp, which I'm guilty of, has resulted in some primer's getting seated pretty deep. But despite the obvious over seating, I have never had one fail to do what primer's are intended to do. On the flip side of that, I have known of a few hand loaders that seem to constantly deal with mis-fires. Whether the falure is in fact the result of not being seated deep enough, is often confirmed when a second firing pin strike lights the fuse. Many springs and firing pins have been replaced only to discover it was a .03 cent primer not properly seated causing the failure.
+1 to BDS for addressing a topic that many will benefit from, and +1 for the informative posts also.

 

[armoredman]

magnum338, thanks for your info, that makes a WHOLE lot of sense with what I feel/see with the Remington primers in my 99% Winchester brass.

 

[LiveLife]

Many springs and firing pins have been replaced only to discover it was a .03 cent primer not properly seated causing the failure.

My hope exactly to prevent unnecessary replacements of firing/striker pins and springs and much less frustration on the firing line.