Primer seating depth and primer seating force

[drop_point]

The key to understanding this article is that he quotes SD based on a three shot sample and that his "primer seating test" consisted of three shots each. If that does not raise serious questions in your mind about the validity of his results then you need to do a review of your statistics class with special attention to sample size.

Exactly. Three round SD data is as much happenstance as it is useful information.

 

[BoydAllen]

OK, I did it, some measuring. NOS Lap. .220 Russian pocket depth, .1215 (Starrett depth mic.); old stock primers, BR4 .120, 205M .122, WSR .1215. I pulled out a box of sized, primed (205) PPC cases, gold box, seating depth of two was -.0095, seated as I always do, at a solid stop. I wish I was in shape to do some testing, because this data begs for a seating depth test. For all of you who seat by feel, how do your primer seating depths jive with calculated touch based on primer thickness and pocket depth?

 

[Doom]

I just purchased that K&M tool after watching the Cortina interview with Dykstra and the Keith Glasscock video on the subject. I also burned 75 rounds testing four levels of crush as measured by that KM tool at 600 yards with a 6mm BRA using Federal 205M primers, I tested -.001, -.002, -.003 and -.004 with 15 shots each and a 15 shot control group seated by feel with my chinesium Frankfort Arsenal hand tool. Chronograph results were obtained with a Lab Radar. Rifle is a 30 inch Krieger shot off bags on the ground with a neo if any of that matters (f class rifle).

PRIMERS	-0.001​	-0.002​	-0.003​	-0.004​	Control "feel"
Average	2911.333​	2908.6​	2917.533​	2915.8​	2917.846​
SD	4.515​	5.225578​	7.957107​	5.062279​	6.174964​
ES	16​	19​	35​	23​	24​

I didn't find these results to indicate a statistically significate trend and found no correlation to vertical performance on target. On to a short review of the tool:

It works for its stated purpose setting crush measured from the height a given primer and depth of pocket (indexed from top of rim to bottom of pocket) for a given case. And it is awful to use, very uncomfortable the handle is a twisted piece of steel that is too short to provide the user with good leverage and the body of the tool is far to narrow to grip comfortably. If you like pain and wasting a lot of time seating primers this is the tool for you. In my eyes I lit 150$ dollars on fire (180$ with the sweet plastic hinged K&M carrying case).

I will test if further at short range to see if there is any effect on accuracy, because I am a sucker for the sunk cost fallacy.

In my 43 years in industry I performed precision testing on a variety of equipment including gas turbines and steam turbines. I took the liberty to run an analysis on your test data since you included it. In comparing the mean (average) velocities using Students T Test the differences in 2 of the velocities are statistically significant, (ie different from the control group). The -0.004 and -0.003 tests are statistically the same as the control. Also the -.001 and -.002 groups are statistically equal to each other. In the case of the standard deviations, using the standard F test, none of the Variances or standard deviations are statistically different.

It looks like you ran a pretty good test. However, one requirement if you were to actually carry this forward would be to perform the test again. Also, you seated the control group by feel which will be hard to duplicate. What would have been better is to have measured the control (after seating) so it could be duplicated and also compared to the other test groups.

What I would conclude from this test is that it appears that the measured seating depth in the range tested has no significant effect on SD as compared to your feel method and that there may be a slight effect on mean velocity.

A note on ES, statistically ES really has no meaning, its effect on SD diminishes as the sample size grows and its value will typically grow at the same time. Remember that it's value only depends on two values which are extremes.

 

[lawrence97]

I just purchased that K&M tool after watching the Cortina interview with Dykstra and the Keith Glasscock video on the subject. I also burned 75 rounds testing four levels of crush as measured by that KM tool at 600 yards with a 6mm BRA using Federal 205M primers, I tested -.001, -.002, -.003 and -.004 with 15 shots each and a 15 shot control group seated by feel with my chinesium Frankfort Arsenal hand tool. Chronograph results were obtained with a Lab Radar. Rifle is a 30 inch Krieger shot off bags on the ground with a neo if any of that matters (f class rifle).

PRIMERS	-0.001​	-0.002​	-0.003​	-0.004​	Control "feel"
Average	2911.333​	2908.6​	2917.533​	2915.8​	2917.846​
SD	4.515​	5.225578​	7.957107​	5.062279​	6.174964​
ES	16​	19​	35​	23​	24​

I didn't find these results to indicate a statistically significate trend and found no correlation to vertical performance on target. On to a short review of the tool:

It works for its stated purpose setting crush measured from the height a given primer and depth of pocket (indexed from top of rim to bottom of pocket) for a given case. And it is awful to use, very uncomfortable the handle is a twisted piece of steel that is too short to provide the user with good leverage and the body of the tool is far to narrow to grip comfortably. If you like pain and wasting a lot of time seating primers this is the tool for you. In my eyes I lit 150$ dollars on fire (180$ with the sweet plastic hinged K&M carrying case).

I will test if further at short range to see if there is any effect on accuracy, because I am a sucker for the sunk cost fallacy.

I think you needed to do this test with the $600 CPS tool that is talked about in the video for this test to mean anything

 

[Titan]

I think you needed to do this test with the $600 CPS tool that is talked about in the video for this test to mean anything

Clearly if I had spent $600 on the CPS tool, I could cut my groups in half per Mr. Dykstra 1:13:00 into the video. Even though unlike the K&M tool you can't account for variance primer height or pocket depth with his tool, so I guess you would have to uniform and cut pockets while indexing the depth of the cut off the top of the rim and sort primers by height before loading.

 

[Titan]

In my 43 years in industry I performed precision testing on a variety of equipment including gas turbines and steam turbines. I took the liberty to run an analysis on your test data since you included it. In comparing the mean (average) velocities using Students T Test the differences in 2 of the velocities are statistically significant, (ie different from the control group). The -0.004 and -0.003 tests are statistically the same as the control. Also the -.001 and -.002 groups are statistically equal to each other. In the case of the standard deviations, using the standard F test, none of the Variances or standard deviations are statistically different.

It looks like you ran a pretty good test. However, one requirement if you were to actually carry this forward would be to perform the test again. Also, you seated the control group by feel which will be hard to duplicate. What would have been better is to have measured the control (after seating) so it could be duplicated and also compared to the other test groups.

What I would conclude from this test is that it appears that the measured seating depth in the range tested has no significant effect on SD as compared to your feel method and that there may be a slight effect on mean velocity.

A note on ES, statistically ES really has no meaning, its effect on SD diminishes as the sample size grows and its value will typically grow at the same time. Remember that it's value only depends on two values which are extremes.

Thanks for the input on the results, regarding mean velocity I suspect the difference is the result of barrel heat and time between the strings being fired. Maybe a better designed test would have been one fired round robin to spread the effects of barrel heat/fouling over all the samples or fire them in a slower cadence.

 

[Doom]

My personal opinion on this primer seating is it ranks up there with charge weight flat spots. To my knowledge no one has put forth a reasonable explanation as to how a variation in seating depth of a few thousandth of an inch can effect the actual performance of the cartridge.

As for target results, most test results posted on forums are the results that support the posters theory or hypothesis. Seldom are the targets shot by someone else who does not know what the test is intend to show. Try as we might, the human mind will work subconsciously to justify what someone is trying to prove.

 

[Rich Hodyl]

Data. Where is Primal Rights' data that PROVES that the CPS produces measurable and significant results OVER any other seating device (such as a 21st Century, etc.)? In the Erik Cortina interview, there were comments made that the CPS will cut groups in half. Half? Let's see the data derived from a test that is actually a legitimate test (rail gun maybe to take out the human element as much as possible, and have the ammunition loaded by someone not involved with the actual shooting of the rounds). Maybe I missed it, but I didn't see anywhere on the Primal Rights website where data is provided, or even mentioned, only things like ergonomics, quality of the construction, etc., which don't get me wrong are all good things. But to make the claim on the Cortina video that it's superior in generating results on the target (which Erik seemed to agree with) - let's see real, statisctically reliable data that backs that up. Just my two cents...

 

[RegionRat]

I won't editorialize the video, it is just FYI

 

[Rich Hodyl]

I won't editorialize the video, it is just FYI

That's interesting. Thanks for sharing that. I am not questioning the premise that primer pocket seating can have an impact on groups, just questioning what is the basis for Dykstra's claim that his product will reduce groups by half versus other seating devices. In this video you sent me, he used a PMA tool and generating some interesting results with that tool - which I think makes the point that the PMA and 21st Century tools and ones similar to those work really well. If the CPS's main selling features are ergonomics and durability, I could see that - but superior in getting results on paper versus the other tools - not sold here on that yet. Anyway, thanks again for sharing the video.

 

[Dusty Stevens]

My personal opinion on this primer seating is it ranks up there with charge weight flat spots. To my knowledge no one has put forth a reasonable explanation as to how a variation in seating depth of a few thousandth of an inch can effect the actual performance of the cartridge.

As for target results, most test results posted on forums are the results that support the posters theory or hypothesis. Seldom are the targets shot by someone else who does not know what the test is intend to show. Try as we might, the human mind will work subconsciously to justify what someone is trying to prove.

Variation of a thousandth of an inch having results is like tuning a carb or timing or any other combustion tuning. There are sweet spots in combustion which has to do with case volume, powder burned, etc and that same seating depth as it relates to engaging rifling- how far it goes before meeting resistance (falls back on combustion pressure spikes and when) and then it affects time of the bullet in the barrel, which if the combustion is good and the bullet time in barrel exits at the same point in the vibration wave of the barrel then it has a better chance of going to the same spot on the target. This is why neck tension comes into play along with how far the firing pin moves the case forward before it stops (consistent bump) and how far the primer moves forward (consistent primer seating depth). Once you study all this and have guns that will show you if something is wrong then it will really open your eyes and have you looking at everything that can possibly affect combustion and time in barrel.

 

[jimmymac]

With all the variables you just listed, none of them matter nearly as much as when the wind bites you in the ass.

 

[Dusty Stevens]

With all the variables you just listed, none of them matter nearly as much as when the wind bites you in the ass.

Well there is that

 

[RegionRat]

In this video you sent me, he used a PMA tool and generating some interesting results with that tool - which I think makes the point that the PMA and 21st Century tools and ones similar to those work really well. If the CPS's main selling features are ergonomics and durability, I could see that - but superior in getting results on paper versus the other tools - not sold here on that yet. Anyway, thanks again for sharing the video.

I have all of them and really like the PMA for the above reasons.

When I allow the handle to bottom on the tool body, I get a fixed stop that I can adjust to a setting point that I reference off of the stats on the brass and the primers.

Until I get things roughly tuned, I attempt a setting that brings the anvil into contact plus 1 to 2 mils. Then plan for taking a closer look once everything else is running well.

I like the Accuracy One gage for gathering the numbers on the brass and the depth setting.

Now that I also have Greg's tool, I really like it because it handles the primers better in those tubes and it is easier from an ergonomics view. If I am not on the Dillon, I still like to make things easy and hands free if at all possible. I had the Holland's adjustable stop modifications on the bench mounted priming tool before I had the PMA tool, and that works almost as well.

Not sure why there is suddenly so much fuss over Greg's tool, but it seems to center on the costs and the free form comments he makes in interviews and videos, instead of the seating depth technology and accuracy testing methods.

http://bulletin.accurateshooter.com/2018/10/darrell-holland-upgrade-for-rcbs-bench-priming-tool/

(Advice to the young... protect yourself from repetitive task injury and bad ergonomics at all times.)

I don't get hung up on small details of what was said in the videos and I might not agree with 100% of what the man says about pocket depths and rims, but I do agree with the general concept that if you start with really low quality brass you make things harder and if you start with really high quality brass you make things easier, and I leave it at that. That primer seating affects accuracy shouldn't be a debate, but apparently this hasn't been well presented or taught lately.

I have had enough trouble of my own at 600 and 1000 to know that primers, pockets, and seating depths really do matter, so to each their own.

If you think this looks controversial, you should see the swirl from 20 or 30 years back in the rimfire world over ignition and accuracy.

Having been in the defense business since the Cold War, I also know that every single primer company out there has had a bad time at one point or another. I just always hope it isn't the batch I am buying. YMMV

Merry Christmas and Happy New Year!

 

[sdean]

This subject has been covered at least 5000 times. Guys at the Super Shoot that I watched use a simple hand tool. They try to shoot 25 shot aggregates under 0.200". I guess none of them know what they are doing.

They only shoot 100 yds. How hard can that be?!!!

 

[Intheshop]

Old Lee round top user here.....

As a voracious student of metrology,I'm intrigued by all this measuring. So,where does, *actual primer cup heights figure in? It would seem that any variation in this dimension,directly effects any other attempt to measure installed height?

* actual,or practical vs print/manufacturer specs

 

[jimmymac]

Old Lee round top user here.....

As a voracious student of metrology,I'm intrigued by all this measuring. So,where does, *actual primer cup heights figure in? It would seem that any variation in this dimension,directly effects any other attempt to measure installed height?

* actual,or practical vs print/manufacturer specs

And lets not forget that each primer needs weighed and broken down in to lots so only those with the same weight are used. Never mind that in order to do this, we'd have to know for a fact that every cup and every anvil weigh exactly the same to be certain the priming compound is the culprit causing the weight discrepancy.

This stuff is a never ending rabbit hole. If it makes you feel better to be buried in the minutiae, then have at it. If you fall on the other side of the spectrum power to you too.

 

[Intheshop]

1930,1st ed. , 1st printing Franklin D. Jones treatise on die making is sitting under our Christmas tree..... wrapped,with my name on it. I know this because I put it there.

I'm interested in gas check "perfection" so understand the concerns with primers.

 

[Mulligan]

Old Lee round top user here.....

As a voracious student of metrology,I'm intrigued by all this measuring. So,where does, *actual primer cup heights figure in? It would seem that any variation in this dimension,directly effects any other attempt to measure installed height?

* actual,or practical vs print/manufacturer specs

The K&M tool measures both cup depth and primer height, to get the exact “fit”.

CW

 

[justinp61]

I'm not a long range shooter, nor an expert marksman by any stretch, but I do like to make my rifles shoot well. I've read this entire thread and watched the video and it appears to me that this a bottomless rabbit hole. The combination of pocket depth, pocket diameter, anvil height, primer diameter are mind boggling to me, not to mention lot to lot variances in primers. I understand and uniform my primer depths, and primer dimensions can be checked and sorted. Then primers seated to a desired anvil crush. But what about the length of the flash port in the brass, for a lack of a better term? If there are variances won't that affect the ignition too?