Witch Doctor: Effects of Primer Seating Depth and Anvil Compression on Precision: UPDATE!

Introduction
In the last primer depth test, we found that primer seating has a major impact on outcome (e.g., grouping). It was clear that a seating depth that placed the primer into the primer pocket at .009” (SAAMI guidelines recommend .008”) was ideal given that the aggregate of the five 5-shot groups was .1992” relative to flush .4282” and .013” .4321. When you examine the anatomy of a primer relative to a primer pocket, you can see that the anvil protrudes beyond the primer cup and when seated at .009” for the particular primers used in the previous test (BR-4), the anvil is compressed .009” but the primer cup itself has .004” clearance from the top of the primer pocket. When the primer was seated at .013”, it was flush with the top of the primer pocket which would have caused maximum compression on the anvil which degraded precision significantly. While I suspect that the anvil compression is the major factor in precision, this follow up explores whether the primer cup itself and its location in the pocket is a factor to be considered. For the purposes of this test, I utilized a CCI 450 primer which has a height of .113” so when seated at .009”, the anvil is fully compressed. If the compression of the anvil is the sole factor in precision, then the CCI 450 seated at .009” should exhibit poor performance similarly to the BR-4 when the BR-4 was seated to .013”. However, if there is an interactive impact of the primer cup height itself and the greater primer cup height somehow compensates for the fully compressed anvil, then the fully compressed anvil in the 450s should perform similarly to the BR-4s which have a remaining .004 clearance to the primer pocket bottom. I realize that these are different primers so there is more than one variable varying at the same time but we will test to see how much variation we could expect from 450s and BR-4s in order to understand how much of an effect that variation would have on the outcome of the main test.
Method and Results
Test 1:
An initial test was performed to assess whether 450 and BR-4 primers would show substantial differences in performance. I loaded 15 rounds with the 450 and seated them flush to the case head to represent no anvil compression. I used the exact same powder, load, bullet, brass, and loading practices as the first test with the BR-4s. I then compared the averages of the three 5-shot groups with the averages of the 5-shot groups from my first test. I realize that this is not a direct comparison because different days can have different atmospheric conditions but I wanted to have at least a ballpark estimate of just how different these primer would perform so that I can estimate how much of a confound this would be with the next larger test. The data showed similarities:
Primer Velocity SD Group
450 3338.3 13.3 .319
BR-4 3352.5 16.4 .387
The point of impacts and group shapes were very similar. Velocity averages were within 15 feet per second, both showed double digit standard deviations, groups were in “the threes,” point of impact was near identical, and group shapes were more similar than dissimilar. Collectively, when factoring in all of the data, the 450s and BR-4s are behaving similarly and I would not expect to see any major variations in their behavior if all else was the same.
Test 2:
50 rounds were loaded with 29.4 of N133 (note that a new lot was utilized for this test relative to the last test because I ran out of the powder from the last test; however, the year is the same but it is a different lot), Paul Parosky’s Patriot bullet seated .013” from the lands, and Norma 6PPC brass annealed and internal necks moly coated. The only difference is that 25 rounds had the Br-4s seated .009 into the primer pocket and 25 rounds had the 450s seated .009.
The same BAT Neuvo rifle was utilized for testing. All rounds were shot on the same day so that atmospheric conditions were relatively constant.
The data showed that the 450 and BR-4s performed the same:
Primer Average Velocity Average SD Average Group
450 3326.2 9.06 .2723
BR-4 3327.2 11.72 .2901
There were no statistically significant differences between 450s and BR-4s on any of the variables.
Conclusions
Building on the previous findings that showed that the anvil compression of .009” was ideal relative to other levels of compression with .003" variance in each tested condition, this test showed that primer cup size and the location of the primer cup in relation to the top of the primer pocket did not have an impact on precision. In conclusion, the anvil compression is the key variable and it is recommended that you compress the anvil at SAMMI specification (.008”) or .009”. Measure your primer pocket depth, primer height including anvil, and primer cup height to ensure that you are seating at the ideal depth and anvil compression.

[@brianhollinger6109]

Thank You Bryan! All of your videos are great. I would never of thought just that little difference in primer seating would make that big of a difference in group size.

[@calebmartinez3805]

You answer all the questions I have the back of my head about primers seating deep, really good job and effort of your part, specially when primers are gold and hard to find. Thanks sir 👍🏼

[@snakeoiler2921]

Thanks for your time. Being new to reloading I find your testing very helpful and informative. I guess I have a lot of screen time to catch up on.

[@markbuckingham6119]

I am so glad to have discovered your channel & really like how you explain everything.

[@Eric-qu3ht]

Thanks Bryan for the test - I like the updated primer dimensions breakdown and your findings are very valuable. I read recently that magnum primers have a different chemical composition over standard primers - they do not pack more of the same compound in a larger cup size. Assuming group size is related to ignition timing, i.e., when the firing pin compresses the primer cup against the anvil, then finding similar groups sizes at the same seating depth measured from the face of the cartridge would make sense (assuming consistent headspace, as the firing ping should push the cartridge against the shoulder first before crushing the primer cup; and also assuming similar anvil dimensions between standard and magnum primers). FYI - I tested BR-4 against 450 in developing a Varget load for a 6 Dasher last summer. At the same seating depth within a node, BR4 gave me tiny groups with an occasional flyer (~20% of the groups) , while 450 groups were a bit larger but very consistent. I re-tested quite a bit and ended up attributing this to more consistent combustion with the 450 for the specifics of my loads. It's interesting that you do not see differences between the two primers - perhaps you load combustion is optimized with BR4 and there is no impact of a more powerful ignition compound? So many factors at play.. not sure any theory can hold!

[@linklesstennessee2078]

Good shooting and good information

[@wvlongshooter3912]

Thanks again for this content!!!

[@BenchAddict-hs1nu]

In this video you were able to conclude on anvil compression as being the key component to precision and having no relation to cup height. In another video on primer sorting you found weight sorting provided significant gains to precision. As we know, overall height in primers varies from one to the next as does rim thickness on the casings. Are you doing anything about primer heights with weight sorting to maintain consistent anvil compression? Also, what about rim thickness variation in the casings? Would really love to know more on this as I've been stuck in this rabbit hole on primer sorting & seating. Thanks and hope to hear soon on this if you get time.

[@WitchDoctorPrecision]

Thanks for tuning in. I really should do a video summarizing all of the results and some things I’ve learned along the way. I’ll add it to the list. What I’ve found is simply weight sorting is a great idea because you will have significant vertical dispersion out to as little as 200 yards if you don’t or you’re not lucky enough to have an incredibly uniform lot of primers. For example, four primers weighing 3.68 will cluster together but one primer weighing 3.60 will drop. I can’t tell you how many times I’ve seen that in matches where there is an “unexplained” drop shot among shooters who do not weight sort. As for the anvil, yes, that is the key variable which is why I recommend measuring your primer pocket length and know the primer cup height and anvil protrusion. I have seen postings on shooting sites of an image that shows primer dimensions of widely used primers in the USA like Federal and CCI so you can get the dimensions from that resource assuming it’s up to date. In a nutshell, you have to have both variables (weight and anvil compression) controlled and then you will get optimal precision. As for the rim height on the brass, yes, you have to be careful with that because those heights can vary quite a bit. What I do is set my primer tool to seat to the depth that gives me .008” anvil compression and then check every primer I seat with either calipers or a primer seating depth gauge. I allow for .001” variance (Speedy Gonzales sets his threshold at .0005”). Any piece of brass that shows variance beyond .001”, I check the brass rim thickness and it’s usually off spec. I use out of spec brass for setting my neck turning tool, setting neck trimming tool, Aztec code on my AMP annealer, and other things but I definitely will not shoot it in a match because my primer seating will be off and degrade precision. I just texted Speedy about this the other day and he has a nifty custom made tool that rapidly measure the brass rim thickness…much more efficient than my method which uses primer depth as a proxy measure. He’s going to send me that tool so I can try it out…I’ll have to give it back but I’m going to use it to see if my proxy measure is accurate enough and I won’t have to make one of those tools myself or find somebody who could. With cups that are thicker (e.g., CCI) than what I’m used to (Federal), the seating force is higher but what I do is seat once, rotate the brass about 120 degrees, seat again, rotate 120 degrees, and then seat again. The primers get seated uniformly with this method. I found with thinner cups, I only have to rotate once but can’t hurt to rotate three times. The thicker cups with more seating force don’t seem to affect precision. One other thing you have to consider is differences in primer pocket design. With Alpha brass, I believe there is some kind of bevel in the cup that I suspect is crushing the primer cup and causing a disturbance to the anvil. This could be why Alpha brass shot worse than Lapua in my testing. Also, a handful of great match shooters told me that once they removed the bevel after reaming the pockets, the Alpha brass shot better but still not as good as Lapua. So, in a nutshell, as long as you get that anvil compressed to .007-.009”, the primers are weight sorted, and you’ve culled out the brass with too much or too little rim thickness, you should be good to go! Thanks for inspiring me to do another video and I hope you shoot small!

[@WitchDoctorPrecision]

I did a quick video on the brass rim thickness issue and there is a direct relationship between rim thickness and seating depth. The thinner the rim thickness, the shallower the primer is seated. I’ll post that video on my Patreon and the maybe do a more comprehensive review on KZbin. I recommend becoming a Patron because I post there a lot. KZbin is just fliers for the concert.

[@BenchAddict-hs1nu]

@WitchDoctorPrecision Thank you for the detailed response. I can't begin to tell you how grateful I am for that information. If you only knew the amount of time, effort and grief that I've gone through to get a straight answer on that. You've definitely made a Patreon member out of me and will look forward to learning more from your testing and will gladly contribute to helping keep that going.

[@WitchDoctorPrecision]

@@BenchAddict-hs1nu welcome to the team! Everything I do is to support shooters by having practical data that answers practical questions. I’ve grown weary of the keyboard warriors, fake experts, pseudo intellectuals, and others who only have conjecture. One test is worth 1000 expert opinions! Follow the data!

[@MMBRM]

Another great test Bryan, Thanks. Although it seems to raise more questions for me because with my lapua 220 russian(fire formed to 6PPC) I've got primer pockets that are ~0.120" deep below the rim and my BR4 seem to measure 0.120-0.1205" with two different calibrated micrometers. I say seem because it's possible I'm compressing the anvil slightly when I measure. However, I'm getting visible metallic deformation of the primer cup before I can get 0.009" of anvil crush(0.009 below the rim). I'm actually seeing some deformation under a loop at 0.006 below the rim. Seems to me that the cup would be fully seated to the base of the pocket before any deformation is taking place. It's taking a lot of force and literally bottoming out my hand primer before I get over 0.008" below the rim. I'm going to check more calibers and brass over the next little while to see if I get a correlation between them. I am convinced that I definitely need a primer seater with a physical stop at this point in any case. Guess I've got a new machine shop project! Merry Christmas to you and yours!

[@WitchDoctorPrecision]

Good luck working that out! I like the idea of a primer seater with a definitive stop point. Should help with uniformity and prevent accidental cup crush. Happy holidays!

[@dinoc.5537]

Merry Christmas and Happy New Year Bryan!!! And thanks for sharing your hard work!!!

[@WitchDoctorPrecision]

Thanks! Merry Christmas to all!

[@pstewart5443]

Really good work, sir. Appreciate all the time & effort put into these. I've gotta find me a LE Wilson case check and micrometer in stock so I can verify where my primer depth is at. Had been considering it and a Primal Rights seating tool, but couldn't justify that price point no matter how well it works. Just been using the Dillon to seat em.I push em in far as theyll go and that has worked to make it go bang, but at 1k, the greater amount the data, the better chance one has of knowing where the shot is going when the shot breaks.

[@juliusjames5577]

Thanks!

[@toddb930]

Thanks for the info!! I've got some testing to do. 🤪

[@roblongridge9698]

It seems this test confirms that primer seating depth is about ignition timing vs anvil crush. Indexing off the case base to a depth of .009 means the firing pin strike is at the same distance from the bolt face….

[@br4713]

Really interesting but for me the most interesting is the velocity consistency vs primer seating depth.

[@Chuck_Carolina]

Nice work: did you talk to a Primer Manufacturer to see what they design into the seating of one of their primers? Nobody to date has set up an experiment and come up with a result they didn't expect - so let me ask you? What did any of you learn?

[@WitchDoctorPrecision]

Please place the links or references that I can review of these experiments you mention and the experimenter’s expected findings. On the topic of expectations, I purposefully did not seek information that would lead me to expect anything. I also used, as I do in many of my other tests, procedures that blind me to what I am shooting. It is called the empirical approach to designing experiments and it eliminates certain biases that can arise with expectations. So, I guess I did not do this experiment the way that the people you describe conducted theirs.

[@bob1764]

In looking at the SAAMI specs on page 36 it states that primers to be seated FLUSH to 0.008" below the face of the cartridge case head. So there is a range but I can't find where it states that the ideal is at exactly 0.008.

[@rload4374]

Great info! I really appreciate how you record all data and analyse it! Question, how can i reach you for the sheet of your previous video? I can’t sand an email by yt… Have a nice Christmas!

[@WitchDoctorPrecision]

PM on FB

[@rload4374]

Message send 👍profile name is the same

[@zoidelux]

I can’t help but notice at 8:40 it looks like the two groups on the right are exact mirrored images of each other?

[@WitchDoctorPrecision]

They must be because I just looked at the target in person and didn’t see one shot with the 450s that looked like the mirror image. Click error when pasting over? Or I write down that I was going to make some point of the mirror image but didn’t? Don’t know but the point is simply that POI was the same with the 450s and BR-4s and so they can be used to assess cup location effects vs. anvil compression.

[@zoidelux]

@@WitchDoctorPrecision yea, i dont mean to point out the weird things but maybe you want to know to point it out so people aren’t confused… just tryin to help, i just shared this video with my uncle this morning, he’s been a shooter his whole life and is still amazed at the new things people are doing like primer seating depth. You’re by far the most concise and professional testing youtube channel, Im really amazed at the detail of all this.. do you publish the papers you’re writing somewhere?

[@WitchDoctorPrecision]

@@zoidelux thank you for the feedback. Based on feedback I received including yours, I do want to publish this stuff in a book. It will enable me to stay organized with information, provide more info relative to a video format, etc. Basically, a book would enable me to put as much of the info out with the least amount of errors.

[@zoidelux]

@@WitchDoctorPrecision heck yes! Do you have a patreon? Many people would pay for your hard work and dedication!

[@WitchDoctorPrecision]

@@zoidelux I do but I haven’t had much time to develop it beyond simply creating one. I plan to get back to it and beef it up. Thanks for the suggestion and encouragement.

[@zoidelux]

First off, holy crap, unbelievably amazing stuff, I would pay money for this stuff.. I just have one thing im confused and dont take this as criticism please, i don’t intend it to be, im just confused at the fact that the br4 is anvil crushing at 9 thou now, but in the last video it was not crushing at 9 thou? It was just bottomed out in the pocket? In the first video you said br4 primers are .1135” but in this video they’re .122”? Im probably missing something i dunno, just trying to understand it correctly. Absolutely love the channel, my mind is blown

[@WitchDoctorPrecision]

I must have misspoken. I do that from time to time when I have a bunch of numbers rolling through my head. I am getting better with that by writing scripts for the videos. What I meant to say was .1135 is the cup size but .122 is the overall length which includes anvil protrusion and cup length. Thanks for listening carefully and catching that. Keep doing that so I can keep finding ways to improve my communication!

[@justinkolander4526]

Did you have much/any cup deformation when seating the 450s that deep? If so, is that a concern or not?

[@WitchDoctorPrecision]

No, didn’t notice any deformities.

[@ZZ-uf4zv]

So are you saying to seat the primer till the primer anvil touches the top of the pocket based on overall measurement, then compress it further into the primer .009" more?

[@WitchDoctorPrecision]

Yes, exactly. I would try .008 of anvil compression too because those shot well when I shot a couple groups of them the other day. The reason why I concluded this was because: The BR-4 performed best at .009 and very poorly at .013 The BR-4 at .013 is where the anvil compression is at .013 and the top of the primer cup is flush with the top of the pocket and it shot poorly so I wouldn’t simply seat to the top unless you have a primer like the 450 which, when seated to the top, is .009 anvil compression and it performs the same as the BR-4 with the same compression. This is why I would measure everything and then focus on anvil compression rather than seating depth and/or seating to the top. If it just so happens that seating to the top and/or by feel is .009 then great but if it’s not, then you may be leaving precision on the table.

[@semaki24]

@@WitchDoctorPrecision Its looks like some primers (BR-4) is sensitive for seating depths, and some like (450) is not sensitive.

[@bob1764]

I just measured a dozen CCI450 primers and they all were 0.119 - 0.121" in height. I did not find any CCI 450 primers that had a height of .113. What do you think accounts for this discrepancy?

[@WitchDoctorPrecision]

Cup height is .113. Cup and anvil height is what you are measuring.

[@bob1764]

@@WitchDoctorPrecision Thank you for the clarification. So anvil height sticking out beyond the top of the primer is ~ 0.006-0.008 or so with the CCI450?

[@WitchDoctorPrecision]

@@bob1764 yes, around .008. With the 450, you can simply “bottom out” the cup to the ceiling of the primer pocket to reach optimal anvil compression whereas the BR-4 requires precise seating because the cup is shorter.

[@huntmulies39]

Thank you I didn’t know I was confused until I seen this video. I thought you were saying anvil compression was crush you meant cup compression was crush if I’m understanding correctly. Love the testing if only I could waist ammo on primer testing the world would be a better place.

[@WitchDoctorPrecision]

Sorry, I must have mixed terms. I really mean compression. Compressing the anvil .008” or .009”. I wouldn’t crush the primer cup. I’ve seen a lot of ignition issues when a cup get crushed either vertically or horizontally.

[@davidmckey8662]

Really ennoying these videos on seating depth. I am new to this level of testing. My question are. What amount of variation in pockets depth is excepted? When I measure my primers. I am finding , 7 to 9.5 thousand between anvil and cup measurement. I assume not to crush the cup is correct?

[@WitchDoctorPrecision]

Thanks for tuning in! I’ve found that pocket depth variation depends on some factors including brand and whether it was uniformed. In high quality brands, I usually see .002” variation among a lot of 101 pieces. It seems like a little variation does not have a major impact on precision for the type of shooting most people do. But if I were shooting ELR at 2 miles, then I’d make sure my pocket depths and primer cups are perfectly uniform so I can compress the anvil .007-.009”. And, yes, do not crush the cup. There is a certain brand of brass the has a bevel in the primer pocket which slightly crushes the primer and this causes major negative effects on precision. After I cut the bevel out of the cup, precision improved. I would be careful what brass you use.

[@davidmckey8662]

@@WitchDoctorPrecision thanks for the reply!! I use lapua brass, small primer. My first lot, the pickets were shallow so I uniformed them. The next couple of boxes I got were deep. Started at .122.5 and .123. My understanding is that as you shoot them they should get more shallow. Not happening on my brass. Thank you for the help!!