How and why to sort primers

[tricrown]

The widely know stuff:

Sometime back I was watching a Discovery or History Channel show on guns. There was a segment of the show where they went into a reloading room used by the Marine Corp. There among the CoAx presses was a young gent sorting primers by weight. Now I’ve already started into sorting my primers, but the first thing I thought of, as any former sailor would, is if the Marine Corp is now sorting primers how much further along would the Navy be?

Both the Lapua and Speer manuals give dimensions for primer seating. The Lapua manual says to seat them “usually 0.1 … 0.2mm below flush” depending on primer pocket depth. The Speer manual says “CCI primers provide optimum sensitivity when seated .003” to .005” below flush with the anvil legs in contact with the bottom of the primer pocket.” But those numbers are just a rough guide as to where the properly seated primer should be resting. The key here is not just having the anvil contact the bottom of the primer pocket, but as a CCI tech told me you want to have .002” compression of the anvil into the primer mix. That kind of preloading makes for the highest degree of primmer sensitivity. With that in mind my high precision reloading is now done using a K&M with dial indicator that allows me to feel the primer hit bottom and than compress it another .002”.

There’s an average of .008” difference in primer height in a brick. So if you’re seating by using a set depth below flush as your goal instead of using feel you run into the risk of seating to deep or seating too shallow. If you seat a primmer too deep it may not go off at all. If you seat a primmer to shallow you’ll have the firing pin finish seating the primer against the bottom of the pocket before it sets it off. Either way you’ve caused a more erratic firing sequence.

The not so widely know stuff:

Now if you were to weigh a box of 1000 primers with a scale capable of reading to a couple hundreds of a grain you’ll find somewhere around .2g difference between lightest and heaviest primers. My original thinking was that most of that weight variation must lay in the difference in height and that was caused by the cups. Ah, but not so as I found out when I came around to re-weighing those same fired primers.

The cups and anvils of every fired primer I’ve weighed came to within a few hundreds of a grain of each other. The cups even all measured to within .001" the same height once they were fired with no powder. I took the lightest and heaviest primers from a brick of small rifle CCI Mag, CCI BR, & Federal Match. After firing these primers that had weighed as much as .2g difference unfired they were now down to within .04g of each other fired. Coincidently, the light and heavy of each make were all within .001” height of each other before and after firing. So where’s the weight difference lay?

A call to CCI got me a tech that came to the same conclusion I had. The only place the variation could exist is in the priming mix or the sealant. And since the sealant is a much smaller part of the two, the priming mix is where most of the variation lays. He also told me the BR primers are primed with a greater care when it comes to the mix weight. Roughly the process goes, mixture first, sealant on top, and then anvil is laid on them both. Which explains why the anvils are uneven and the cause of most all of the height variations.

So what’s it all mean? If you are concerned enough to weigh your powder charge down to .02g, why would you want to ignore a potential difference in the .2g difference of priming mix that is lighting up your powder? I had seen a study done a while ago regarding chamber pressure variations between light and heavy primers of the same lot. The effects were more significant then that you would get from the same variation in powder weight.

With a GemPro 250 I can get through a brick of primers in the time it takes the Penguins to take 2 points from the Flyers.

 

[Boyd Allen]

So can we expect to see you post the results of your chronograph test? Also, with the possible exception of the Russian primers, I believe that priming mixture is placed wet, and shrinks as it dries. This probably explains the need to seat slightly deeper than the depth at which the anvil feet make contact.

 

[tricrown]

Boyd, it’ll be a while till I get around to testing them. I’m hoping someone reading this will remember seeing the article about the different pressures from different weight primers. I kinda remember it being something like a study by some university and some military officer.

There’s also a forum member here, don’t remember who it was, that found that different primers, and it may have even been different lots, like a different amount of crush. I think the important thing is the amount the tip of the anvil travels into the mixture.

I tried sorting by the position of the anvil. But the dang things are every which way and too hard for me to see right. Even had some tools made for a bullet comparator? One was a small cup to hold the primer and the other a ball bearing sized so it could measure at a point down the anvil legs. Sorta like the dial indicator on the K&M does.

I’m guessing the K&M used as instructed would work better than anything if the anvil legs are inside the cup. Otherwise if you seat like I do, where I just seat to contact and add .002”, you’d be setting the crush off the cup instead of the anvil. I’ve no idea how critical getting the right crush is. Maybe someone will chime in that has experimented with it.

 

[mike in co]

"A call to CCI got me a tech that came to the same conclusion I had. The only place the variation could exist is in the priming mix or the sealant. And since the sealant is a much smaller part of the two, the priming mix is where most of the variation lays. "

assumptions that the sealant is not the source of the issue will bite on on the rear cheeks....

lets us know how it goes...

mike in co

 

[mikecr]

You're not using the K&M by the instructions. There is no 'feel' to the correct process(which is far more accurate than possible by feel)..
Instead, there is zeroing the indicator off the specific pocket bottom as biased by the specific primer height to seat.
That is, you place the primer face down under the indicator anvil(on it's shelf), you slip the case into the shellholder, and then squeeze the handle all the way. While here you zero the indicator, release the handle, remove the shell, lift the indicator anvil off the primer and put the primer in place to seat. Replace the same case zero'd and seat to your zero + 2thou crush (at least).
Repeat the seating cycle to ensure that the primer is springing back to your crush setting as indicated.

Different primer brands, firing pin settings, and trigger release do cause optimum crush settings to change(as validated over a chrono & target).
There is also a matter of time reloaded to intended use of the ammo, and pocket tightness, as primers back out over time much like sized brass further springing back over time.
Also, there is a potential matter of primer depth to casehead -vs- primer depth to specific crush. These can only be matching when pockets are exactly the same desired depth.

I haven't weighed or tested weighed primers because I did not know where the variance was coming from.
I have a ton of testing to do otherwise though.