Primer weight sorting discussion

[John Weigel]

A closer look at primer sorting

Disclaimer: Yes, I know that wind interpretation skills for F Class shooters (and me in particular) outweighs the frivolous pursuit of tiny groups at short distances, but still… As a compulsive experimenter, I can’t resist wasting ammo and time driving to and from short distance shooting ranges pursuing load accuracy. Besides, it’s a lot harder to get opportunities to work on wind calling. I'm trying.

Over the past couple of years, especially during frustrating Covid shutdown period, I tested a whole bunch of load development presuppositions in the pursuit of super tight groups for a stupid number of rifles and barrels – most tests merely validating current thinking. But there have been some surprises as well, and I thought that I might post some of these on this forum over a period of time, if there is any interest.

I thought I’d first put a toe in the water with a progress report on the question of whether or not primer sorting is worth doing. I’ll attach some data and targets with this post for anyone interested in where I’m at in trying to answer this question. But here’s a summary of what I’ve noticed so far (see tables they draw from below).

• Within a single brick of 1,000 CCI BR2 primers, I found (only) a 6% variation in primer weights. Interestingly, the ‘bell shaped’ distribution curve is not steep; pretty evenly distributed between 5.18 grains and 5.40 grains (4% variation only). Only about a half percent of primers fell outside this distribution, and those only fell just outside this range.
• I fired 10 weight classes of primers (5.14 gr – 5.44 gr), mostly in groups of five shots to measure MV variation, and to retrieve and weigh spent primers. Attached targets indicate noticeable variation in five-shot groups, but I wouldn’t put much emphasis on these results, as the rounds I fired were all with loads previously tuned for 5.30 grain primers – and adjustment of seating depth and/or tuner may well accommodate any of the primer weight classes I tested.
• Although I found a relationship between primer weight and muzzle velocity (the heavier, the faster), it’s not yet as clear as I expected it would be (eg lighter powder charge - 50.7gr ‘new type’ 2209 was more affected than slightly hotter load with 51.0 grains) and may be as little as 10-15 fps between for higher pressure loads. I’ll keep testing, and will try Federal 210GM and Federal 215M magnum primers (carefully) to see how they compare in some respects.
• The most surprising result, and perhaps the only real takeaway from this post is the dramatic variation in weight of explosive component (plus anything else that is consumed in ignition process). Retrieved spent primers were remarkably consistent in weight, varying only 2% and did not reflect pre-fired weight distribution. But when spent cup and anvil combo weights are subtracted from pre-fired weights, the variation is a whopping 58%. That’s a lot of inconsistency in the application of ‘active ingredients’ for a premium primer, no?
•
Running parallel to above ‘to sort, or not to sort’ primers testing, I’ve been experimenting with incremental enlargement of primer flash holes with expensive and hard-to-find drill bits. I’d previously extensively tested the effect of primer seating depth in load development - which is considerable - at least with my 284 Win Lapua brass and CCI primer combo. -I’ll make a report in the future if it is of interest. I’ve been holding off because I think there’s another dimension to this question, and I’m testing it now. I think that the impact of shifting primer-seating depth may relate at least in part to the sharp angle of case-intruding explosive primer action passing through the tiny flash hole. I’ve been testing incremental enlargement of flash holes. After all, what is so sacred about the ‘large rifle’ 0.08” flash hole diameter? Was it based on experimentation with modern powders and primers? What I have already seen is a much bigger impact upon ignition dynamics and a resulting improvement ES/SD (and tune, using barrel tuner only).
I’ll let you know if and when I’m able to prove anything. On this question of flash hole expansion, I asked the Americans on the Accurate Shooter forum whether anyone had tried it over there, someone dug up an old Masters thesis dealing with primer ignition. That paper indicated that the experimenter found improved accuracy with enlarged flash hole. I guess there are no new ideas.

Attached: a couple of summary tables re primer weight experiment – so far. Also targets with speed data. Shot over two sessions at St Mary’s indoor range.

[RDavies]

Good to see someone put in this sort of effort and keen to hear results of your primer seating test.
One suggestion is to test not so much seating depth of primers, but the actual crush which will vary for each different primer.

[John Weigel]

Thanks Rod, coming from you, encouragement takes on a special momentum.

I've loaded up another wave of test cartridges tonight, with Federal GM (210) primers, Federal 215 Magnum primers, and two more experimental loads with expanded primer pockets (2.15mm and 2.25mm). I'll take my usual bench at St Mary's tomorrow morning - they all know me there by name. If I have any unexpected results I'll post on this thread. BTW, despite the strange variation in colour that characterises Federal primers on the under-cup side, (I wrote the manufacturer a year ago and got just a 'don't worry, they are fine' response), the 300 primers I sorted by weight tonight were confined to a narrower range of variation than the CCI BR2 pattern. Will be interesting to see what variation in explosive and consumable stuff (coating?) is within the three weight classes I've chosen to shoot. I don't expect small groups without tuning from scratch with these different test scenarios, but velocity consistency and speed trend in the first instance is worth checking out. Starting with light loads with the magnum primers, but have hotter loads ready to incrementally test pressure increase, with heavy bolt lift enough signal to stop.

[Downes Equestrian]

Love the testing John. I competed at national level benchrest for a while when I was younger and so it has made me totally anal on checking stuff. The tradeoff is time lost for small improvement if any, but your testing seems to be pointing to a measurable improvement, so hay go your hardest and keep us informed

[Rich4]

Great stuff, just wondering if you cleaned the spent primers before weighing?
Thus ensuring you only weigh the cup and no variation went down the bore?

[PeteFox]

John
Primer weights - one of those rabbit holes that never ends - some observations.
The success of your experiments (actually finding out something worthwhile) will be largely dependent on your experimental design - making sure that you are measuring the variable you want to measure rather than something else.
I am not trying to be negative, just realistic. Sorry for the convoluted language


If you think that the souce of larger groups is ignition variability due to the priming compound, is it the amount? or in the mixture itself? (separation of, or variability in the mixture).
Could it be cup thickness? primer seating depth? or gap between cup and anvil? or perhaps not all falls of the firing pin are equal

I don't think the percent weight variation is important, given that each primer you weigh has a cup and an anvil, made from metal and that is where the overwhelming portion of the weight will be ( I think). So if you are graphing percent weight, the curve will be relatively flat (if the metal weight is consistent)

If the important variation is in the amount of priming compound, then:

Separating the priming compound weight variability from any variability in the weight of the metal parts is the big problem and has always been the stopper for me - as in the thing that stopped me from weighing primers.

You could collect old primers and try to clean out the carbon etc (some nasty chemicals needed here) and establish some baseline weight varaibility data for the metal parts- where that would lead I don't know, because you will still have variability between whole primers but you won't know the source of the variability; unless you can establish that the variability in the weight of the metal parts is neglegible.

In short you need to eliminate some primer parts as a source of weight variability, otherwise I think you are wasting your time.

Perhaps weighing primers and just discarding the outliers might be enough?

Pete

[JezL]

John,

Not sure if you have come across Bryan Zolnikov on youtube. His Witch doctor series has a few videos and testing based on your findings also. Might be worth a good comparison against your results for common trend ?
This is his video on primer weight testing federals.
https://www.youtube.com/watch?v=uUg_wkz ... anZolnikov

tldl; From his desription. ....
The purpose of this video is to display the results from primer weight sorting tests using Federal 205 and 205M primers. Results showed a linear trend whereby heavier primer weights exhibited faster velocities. The 205Ms demonstrated better ballistics (i.e., velocity standard deviation and extreme spread) relative to the 205s. Results suggest that match or benchrest quality primers are likely to outperform standard primers and benefits can be gained in groups size by weight sorting both the standard and match primers

Great work John!

[John Weigel]

It looks like I dumped too much theorising and speculating, as well as content in my post. Here are a couple of responses to the comments. If you cut through all the stuff I said, the only relatively new finding is that in the CCI primers I tested (so far), the old concern about whether or not the weight variation in primers might just as well be attributed to variation in the cup and anvil didn't bear out. Those components varied very little - almost not at all. Nearly all of the weight variation in my samples can be attributed to the non-metal components - namely explosive, and any secret sauce additions - eg are there any coatings? I found a ridiculous 58% variation in these consumables across the sample. It was also clear that muzzle velocity increased with increasing weight of primers (i.e. amount of explosive/consumables). What surprised me, given what Brian Zolnikov and others have expressed much better than I did, is that in the two powder charge tests I did, was that whilst the slower (50.7gr 2209) batch followed the results of Brian's and others' tests, in a batch of 'hotter' cartridges (51.0gr 2209), that speed difference was less profound, maybe only 10-15 feet per second across such a vast variation in the weight of explosives/consumables.

Although I referred to primer seating depth tests I've done before, I didn't spell the results out very well. I'll do that in a separate post. My tests followed those of Brian Z and Erik Cortina of a year or so ago, and pretty much supported their findings. And I agree with what Rod Davies said regarding contact point of primer cup and end of primer pocket tunnel being the real data point to experiment from. Surprisingly, both Brian and Erik did not mention that contact point nor amount of crush. Their data point was 'flush with case head' inwards.Since I uniform primer pockets, and would expect variation in my point of contact and perhaps someone else (and there may be variation in batches and brands of brass) I pushed both of them via emails for a figure, (how far beyond flush with case head and contact with other end of primer pocket - the start of crush), but neither responded. I found my contact point to be at 0.003 beyond flush with case head. And not to get ahead of myself too much, I found that less than contact was hard to tune for, but could be made to work, and any amount of crush would similarly work - but that you have to tune load AFTER establishing your primer seating depth and sticking with it. Hard to believe that variations in crush can ultimately affect barrel harmonics, but go figure.

So yes, nothing new in my post above, other than that it looks like weight variation in primers tested (CCI BR2) can be attributed solely to their non-metallic components, and most likely the explosive element. BTW I weighed intact spent primers, then pulled out anvils and shook out charred (carbon?) contents, and even brushed anvil and cup before re-weighing. That slag component proved to weigh next to nothing - but I do have a second data set that shows that, if it is of interest. The weights I gave were of cleaned cup and anvil combos.

[John Weigel]

Yikes. How's this for timing. Brian Z just released a video on primer flash hole expansion on Accurate Shooter. He did test on small primer brass and found no MV improvement. He did not attempt to adjust his tune to see if new accuracy node lay elsewhere.

[RDavies]

Although I referred to primer seating depth tests I've done before, I didn't spell the results out very well. I'll do that in a separate post. My tests followed those of Brian Z and Erik Cortina of a year or so ago, and pretty much supported their findings. And I agree with what Rod Davies said regarding contact point of primer cup and end of primer pocket tunnel being the real data point to experiment from. Surprisingly, both Brian and Erik did not mention that contact point nor amount of crush. Their data point was 'flush with case head' inwards.Since I uniform primer pockets, and would expect variation in my point of contact and perhaps someone else (and there may be variation in batches and brands of brass) I pushed both of them via emails for a figure, (how far beyond flush with case head and contact with other end of primer pocket - the start of crush), but neither responded. I found my contact point to be at 0.003 beyond flush with case head. And not to get ahead of myself too much, I found that less than contact was hard to tune for, but could be made to work, and any amount of crush would similarly work - but that you have to tune load AFTER establishing your primer seating depth and sticking with it. Hard to believe that variations in crush can ultimately affect barrel harmonics, but go figure.

After reading some articles on primer crush a few years ago I bought one of the primer tools with the dial indicator, where you first zero the indicator to the depth of pocket and thickness of the primer, then you take the primer out of the zeroing position and put it into the seater watching the dial indicator to give 5 thou crush with LR primers. (3 thou with small primers). I used these numbers after reading a few articles about 10 years ago where tests found those to be the best amount of crush and also where primer manufacturers recommended.

I havent done any testing on different crush personally but I think it was Eric Cortina did mention it recently (Or was it Brian Litz???). One thing I do remember though is at the range one day helping a new shooter with his rifle, some shots were not going off and ES was terrible. I found the primers were seated much more below flush than I was used to. He indicated that he seated the primers as hard as he could and so was likely crushing them too much. This might be an extreme example but how much crush starts to worsen ES/SD would be a good test for you to try again if you felt like experimenting more.

[John Weigel]

I've tested the effect of primer seating depth a few times - and will so a bit more testing at 5 thous plus to extreme crush soon. Here's a sloppy looking target from back in early July that gives a not-even-close to statistically significant peek at what I found re speeds at less-than-contact up to crush plus 4.5 thousandths. Straight 284 Win. Mostly 4 shot groups only - my usual. Ignore targets 1-4, other than that all shots had primers (CCI BR2) seated at 4 thous from case head which meant precise contact with end of primer pocket channel. Targets 5 onwards at least hint at little, if any change in MV between 1.5 short of crush and 4.5 of crush. Again, I wouldn't read much into accuracy, as it only pertains to the default load I was playing with. What might be more interesting for some, though way off topic, is the hinted-at improved ES for lubricated necks vs non-lubed (graphite powder), though less accuracy (until I purpose tuned to accommodate graphite-powdered neck lube, which was easy.

After yesterday's test with Federal GM LR primers, I'm definitely going to switch from the CCI BR2s, as ES with the Feds was much better. I wish I'd tried them earlier with my F-class rifles. Dissected after-shot cups and anvils of Feds were as consistent as with the CCIs, but overall weight variation of unfired primers was much tighter in the Feds, which meant variation in explosive/consumables was correspondingly much less variable than the CCIs. Also, rounds that I shot yesterday with magnum primers went much faster (20fps), but look promising with reduced powder charge (for me, 50.7 2209), and I'll fiddle around more with this stuff before putting up a post on this forum.

[Pablolig]

Hi Rod and John,

Silly question:
By saying "primer crush" are you referring to the depth of the primer compared to the base or the case?
In other words, for a LRP are the 0.005" measured from the base of the case to the bottom of the primer?

Thanks!!

[RDavies]

Hi Rod and John,

Silly question:
By saying "primer crush" are you referring to the depth of the primer compared to the base or the case?
In other words, for a LRP are the 0.005" measured from the base of the case to the bottom of the primer?

Thanks!!

.005” crush means the primer is pushed in an extra .005” after it bottoms out in the primer pocket . So if your pocket was .130” deep and your primer before crushing was .125” thick, it would end up being.010” below the surface of the case when fully seated

[Pablolig]

Great!
Thank you

[Aus9914]

Hi John,

Interesting thread. A couple of observations from my perspective FWIW, and first post here so please excuse assumptions on my part.

Firstly - primer flash holes. There was a study done in the US in the mid 90's that found that a smaller flash hole made a positive difference. To such a level the author was able to convince Lapua to make special 308w cases and the US team to use them in the upcoming Palma Match. Those that were on the Fullbore Forum at the time might remember the name of the shooter that did the trial - name escapes me ATM but he was recognized as a top shooter. Flash hole size may very well be a case volume related dimension as if you have looked inside an artillery/tank rnd you will see a spike that is there to help the primer initiate the main charge. So what you find may work for similar volume cases but not necessarily transfer across to other calibers. BTW If you are not already, you might want to also consider deburring the inside of your flash holes - more to follow below.

Secondly - primer seating depth. The most important thing with primers is that they are seated to the bottom of the pocket and consistently ignite the powder column....Taking a few steps back we need to be cognizant of how the primer is initiated first. I ran a trial/test for my rifle club in BNE on quality control of handloading of ammunition and its implications on both the individual's as well as the team's results about 10 years ago. During the QC check of club members ammo it was found that primers in some samples where proud of the case head and others claimed theirs were all seated to within .001", others cut their primer pockets and others didn't. While it was also found in some cases there was a significant variation in case headspace dimensions relative to their chamber's dimensions and the rest of their loads. As the priming compound requires a specific level of kinetic energy to initiate it, having what available energy the firing pin has to push the case forward in the chamber, or to complete the seating of primer, or to hit the primer at different distances, you are not going to get consistent ignition of the powder column which will affect muzzle velocities and will in some cases result in miss fires. This is particularly more noticeable when the firing pin has such a short distance to travel between cocked and fired as in 4 locking lug actions, and/or the firing pin mass has been reduced - read alloy body for firing pin, and/or the firing pin spring has lost a lot of it's free length from being compressed for too long - read Omark.

To use a motorsport analogy the practice of "blue printing" your cases by cutting the primer pockets to a consistent depth is a sound practice - but you also need to ensure your case headspace matches that of the chamber and that the flame front from the primer is not masked by burrs within the chamber. I think it was on the US long range forum or in Precision Shooting magazine in the 90's there was some high-speed imagery that showed the flame from different primers through deburred and as bought cases.

Has your study looked at the consistency in height of the primer and the height of the cup and anvil of the primer?

regards
Al