Primer Seating Depth

I use the RCBS ram primer on top of my single stage press to seat primers, and then I measure the depth of most of them. I’m a bit surprised with the amount of variation I see in primer depth, even though I am using calipers and not a depth mic. Measurements can range from flush to 0.006”… which is triple the range in overall case length I get.
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I think the root cause is variation in the case flange thickness. I’m using an RCBS case holder. Is there a tight & precise fit case holder to hold this better, or some other means? I might sort out the brass with thin flanges.
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I understand this may not be a meaningful issue, but reloading is where I get to let my OCD run wild :)

As long as the primer sits inside (below) the plain of the case head, you're fine. Firing pin will find it! All sorts of things reloaders do to primer pockets (swage, deburr flash hole etc.).

I use the Ram Prime from both RCBS and Lyman for all my priming needs in 34 different calibers. My goal is to seat primers .004" below flush, so as to fully seat the anvil into the priming pellet.

Variations in priming depth can be caused by the depth of the primer pockets, or most likely, the variance in the thickness of the case rims. Some brands have slightly thicker case rims than other brands. One brand (new Blazer .38's) doesn't even have an extractor groove turned into the case above the rim and has a relatively thin rim. Those work fine in revolvers, but give fits when trying to eject them from lever action rifles in .357/.38 caliber.

As long as the primers are seated fully to the bottom of the primer pocket, and don't extend above the base of the case, they will go off. Seating to the bottom of the primer pocket sets the anvil to the right depth when the legs of the anvil are even with the open edge of the primer cup.

Hope this helps.

Fred

There is a fair amount of difference in primer pocket depth even in one batch of cases. I have a Sinclair primer pocket cutter that cuts pockets to a preset depth. Some cases cut quite a bit and others don't completely clean up. I seat primers firmly on my presses and they are flush or usually a bit deeper than flush.

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Originally Posted by Dieselhorses

As long as the primer sits inside (below) the plain of the case head, you're fine. Firing pin will find it! All sorts of things reloaders do to primer pockets (swage, deburr flash hole etc.).

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^^This^^

Once, I had several rounds that didn’t fire. I sent them to the primer manufacturer and they responded saying the primers weren’t seated deep enough and that they needed to be 0.005” below the head. I began seating primers more aggressively and have not had another FTF.

I prime all my pistol ammo on 2 Dillon and 2 Lyman TMag presses. I’m not gentle and seat them until they stop moving. My rifle ammo is seated with a hand primer [have old lee auto primes set up for small and large]. I am very particular to make sure they seat all the way. Doesn’t matter if they are flush or below, only that they are seated to the bottom of the primer pocket and of course are not proud of the case base.

Seat to bottom of pocket. Flush* to .008" below the case head, is ok. Seat by feel. Don't use the press as a stop for the depths.
I use the RCBS Ram Prime.

Had some 38 Special brass that needed pocket depth uniformed, to fix protruding primers.

When I started reloading in 1969 I took apart a primer to see how it worked. I figgered it wouldn't work if the anvil wasn't solid against the pocket bottom and allow the compounf to be crushed between the cup and anvil. So ,I seated all the way to the botom of the pocked and I can't remember ever measuring "below surface" seating of any primer in any caliber. I have never had a FTF from a poorly seated primer...

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Originally Posted by 243winxb

Seat to bottom of pocket. Floush to .008" below the case head, is ok. Seat by feel. Don't use the press as a stop for the depths.

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Roger that. The small but very real differences in shell holders AND in case rim thickness AND in pocket depth makes using any adjunct seating stop a counter productive effort. Seat primers by feel - at or below flush, but don't crush them - and all will be well.

What I use is irrelevant because there are several tools that fill the need.

Commercial level reloading machines do net seat by "feel". The Star and Dillon 1050 series loaders seat on the downstroke...full pressure down.

I have to seat by feel on the 550 and the RCBS bench primer so I deal with it. I much prefer loading on the 1050 but it does not make sense for short runs.

Thanks everybody. I’ll look into how much variation I have in pocket depth, and work on seating by feel. If I know the range of primer heights and the range of pocket depths, I’ll be able to kniw if I’m doing a good job at fully seating without crushing.

What I’ve read in an NRA publication on commercial centerfire cartridge loading goes along with ReloaderFred and mdi: primers need to be sensitized by seating. The visibly protruding anvil of an unfired primer straight from the package is set high so that the point of the anvil isn’t pressed up against the priming compound in the bottom of the cup. Seating the primer against the bottom of the pocket presses the anvil point into the compound, in close proximity to the point where the firing pin will strike. Impact crushes the compound against the anvil, igniting it. That’s why a high primer may not fire on the first strike, but could on the second: the first time the anvil wasn’t deep enough to get sufficient impact against the compound and cup, but once pushed in, the second go around is good.

A long way of saying that it seems the primer is designed to be bottomed out in the pocket, and that seems to happen when the seating puts the primer below flush. True that with more or less pressure on the press arm (Dillon SDB, that primes on the upstroke), I can get different seating depths (implying no bottoming out) that all go bang, so long as the primer is below flush (the deeper primers don’t look flattened around the edge, so I think it’s deeper seating with more force rather than flattening of a bottomed out primer).

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Originally Posted by mdi

When I started reloading in 1969 I took apart a primer to see how it worked. I figgered it wouldn't work if the anvil wasn't solid against the pocket bottom and allow the compounf to be crushed between the cup and anvil. So ,I seated all the way to the botom of the pocked and I can't remember ever measuring "below surface" seating of any primer in any caliber. I have never had a FTF from a poorly seated primer...

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I always thought you were supposed to seat all the way to the bottom of the pocket, so that is what I have always done. I’ve never noticed any primers noticeably below the surface.

I don’t get the whole “seat by feel” thing, and here is why. I have never crushed a primer that properly entered a primer pocket, never, and I’m not sure it’s even possible. So, seat them using a bit less than gorilla strength to be sure that they are bottomed out and all will be good. If you happen to get one sideways or half in the pocket you’ll mangle the daylights out of it and I generally toss that brass rather than tinker with removing a badly damaged primer, but I’ve also never popped one.

I don’t measure primer depth, it’s irrelevant for me, but I do imagine that things like swaging a crimped primer pocket will leave a little deformation that makes things look inconsistent when that are perfectly fine.

Re read Kevin’s post … that’s all that’s needed on the subject …. Crushing the anvils

I 'uniform' most rifle primer pockets with one of several tools, K&M, RCBS, others. Do not for 9mm, 40 S&W other handguns unless for hunting or 'special' use. Seating to the bottom of the primer 'by feel' is the key to reliable ignition. There is a surprising variation in primer pocket depth from case to case, the older the brass, the more variation. Forty brass is not nearly as uniform as recent production.

I hand prime and just squeeze till it stops.. never had one of my reloads not go off in any firearm.

FWIW, an aside; Quite a while ago I read about "primer sensitizing". Perhaps primers in the '40s weren't as reliable as those today, but it wasn't uncommon for reloaders to "sensitize" or "preload" primers. After seating primer to bottom of pocket, a bit more pressure was added to the primer, a light crush. I had one experience with Winchester small pistol primers not working 100% in one 9mm striker fired pistol. Loads with Winchester primers worked 100% in 3 other striker fired pistols, and all other primer makes worked 100% in the one gun (FMK). Gun was disassembled and bolt thoutoughly cleaned (firing pin and firing pin channel, springs, etc). Gun contimued to work with CCI Fed, and Wolf, Rem, but would misfire one out of 7-10 rounds with Winchester small pistol primers. I remembered "sensitizing/preloading" and seated 100 Win SP primers with my ram prime in mixed brass and added a little "ummmph!" to preload the primer. Next range trip all 100 WSP loads fired 100%. Now whenever I use WSPs I "sensitize" them. No more misfires...

A couple of years ago I had a problem with failure to fire using small pistol Wolf primers in .38 Spec. The gun I was using was a S&W Model 65 that had been modified for pocket carry(hammer bobbed). I was having over 50% FTF. I was attributing it to hard cups in the Russian primers. An acquaintance that engaged in shooting competition informed me that many Wolfe primers were shorter height than normal and required deeper seating. I use a RCBS auto prime unit so added a little extra pressure when seating and failures went away. Good thing since I have an excess of Wolf Small Pistol primers that I stocked up on back when Obama was elected.

I've never tried to measure seating depth but these primers did seat below flush by an appreciable amount.

Has anyone seen a primer that was noticeably below the surface of the case? I haven’t.

I use a Frankford Arsenal adjustable hand priming tool. But instead of trying to set the depth by adjusting the seating post I just crank it up and do it by feel. This is only on rifle ammunition, I load all my pistol ammo on a Lee Turret press and just use the integrated priming system which works great.

Yes all my primers are below flush I run my finger over the primer on loaded rounds . Never had one flush because I believe they need to be below flush.But I will also say I never measured how much below flush they were.

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Originally Posted by GregLaROCHE

Has anyone seen a primer that was noticeably below the surface of the case? I haven’t.

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If I look for it, it’s visible in some commercial ammo. My reloads may not show much, depending on how firmly I press on the ram arm. Match ammo I make a point of seating deeply, using a firm push with both hands rather than just the one, and it’s very easy on those rounds.

It’s a lot easier to feel the indentation below flush than it is to see it.

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Originally Posted by GregLaROCHE

Has anyone seen a primer that was noticeably below the surface of the case? I haven’t.

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Yes, from flush to .008" below, a SAAMI standard.. One was .010" below. All will fire. The RCBS Vernier end is used to measure depth.

This makes it easy to measure.https://www.rcbs.com/case-processing.../16-87305.html

Imagine the disappointment with my new Lyman primer-er. The thing felt and worked great, but left the primer sticking out by, at least, half its depth. It seemed as though a new one needed to be loaded and force the first one up. That worked. I would have tried to fix it by redrilling the hole in the pivoting rod to make it go higher but their pins to hold everything together, didnt want to move. Bizarre item.

always hand primed by feel .they need to bottom out in the case just below case head ,just run my thumb over case to check. personally i like to seat primer, release the pressure, turn case 90 degrees and squeeze again just to make sure.