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Primer Seating Depth

With every priming tool I've used, the case is held by the front side of the rim, and the primer is pressed into the hole from behind. How can you cut (uniform) all of your primer pockets to the same depth so as to make primer seating a consistent and measurable process?
Well then you would need to turn rims, uniform pocket depths, and match primer heights...
Or, use an indicated K&M primer seater, which accounts for everything, and directly measures bottom/crush.
Can someone enlighten me about the need to adjust the seating depth?
Setting the primer to pocket bottom, and then setting a crush value (~2-5thou) pre-sensitizes the primer.
Depending on your gun's striking, some primers may actually prefer a particular crush.
That is, you can be rewarded for finding and setting this.
Like I found with a couple guns that Feds/Wins/Rems prefer 2thou crush, while CCIs prefer 5thou. Feds/Wins/Rems didn't like 5thou.

There are no striking standards that I'm aware of, and I can picture many guns with extreme striking, or loads far into diminished returns, so that primer firing holds less influence on results.
Not to imply this as an optimum condition, I just suspect it's accepted as good enough.
 
There are no striking standards that I'm aware of
There are only very loose engineering design guidelines for ignition with respect to pin protuberance and firing pin impact energy.

TLDR: if you bother to carefully assemble your ammo, don't neglect your firing pin and bolt.

The commercial primer sales generally follow the science/engineering of the MIL world, but only those primers you tend to see with names like 34 or 41 are bound by the external specs. Commercial (SAAMI) primers may or may not since they may not be concerned with slam fire or mil spec temperature requirements. Commercial outfits have not advertised their primer stats in my memory.

Some of the primer sensitivity tests are organized around a dropped mass that hits a standardized firing pin which rests in special tooling above the primer in the test rig. The falling weight will have a settable height, which determines the energy of the impact. For slam fire requirements, primers are not supposed to go off below a certain maximum setting, and then they must go off above a minimum higher one. Sounds simple in theory doesn't it....

In those machines, one can "play" with the firing pin shapes and protuberance and study the primer ignition statistics (and performance).

To mikecr's point, making the jump in relationship between the design guidelines for primers versus what the actual cartridges, tooling, and guns do is another matter all together.

If there was a failure to ignite, or a performance problem for example, investigating the actual protuberance and energy level of the firing pin's strike isn't trivial for the design or the actual gun/ammo. Topics like springs, friction, damping, etc., are all somewhat chaotic when it comes down to business.

Just like the dimensions of the brass cartridge + the primers + primer tooling... present us with a tolerance study that results in a potential spread of seating results... now imagine the study of the tolerances for things like firing pin assemblies, bolts and chambers that all add to that ignition discussion before we can sit down to estimate the high-low ignition values for a design review, and then go into a lab to determine how actual hardware samples turned out.

Getting grunts to maintain their firing pin assemblies according to procedures is like herding cats. Letting them get dirty or contaminating the lube is difficult to account for in a design review or investigation to say the least, and then there is the fit of the ammo to the chamber that also plays a role and this is also where contaminated chambers are difficult to estimate.

If you are getting picky, keep in mind your brass prep (headspace tolerance) also figures into this ignition equation, and there are differences in ejectors and extractors that must be accounted for and maintained. Don't neglect your firing pin and bolt. Be careful not to over/under lubricate your hardware and pay attention after weather or dusty days. There is no point to being careful with primer seating and then being sloppy with everything else. YMMV
 
My question is whether the dimensional relationship between the extractor groove, the bottom of the primer pocket, and the base of the casehead are exactly the same on each piece of brass from a given Lot#? If they aren't, the problems associated with trying to obtain some consistent (i.e. identical) primer seating depth are obvious. Likewise, is the thickness of the webbing exactly the same on every piece of brass from a given Lot#? Primer seating depth is far from being an exact science. If you're so inclined, test to see what your primer seating depth your specific load and setup likes and try to reproduce that as best you can. Just be aware that case-to-case dimensional variance in the regions mentioned may thwart plans to seat all the primers at the exact same depth. Do the best you can and don't agonize over the results once you have done your due diligence.
 
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My question is whether the dimensional relationship between the extractor groove, the bottom of the primer pocket, and the base of the casehead are exactly the same on each piece of brass from a given Lot#?
And to add... imagine if the gassing on a semi isn't right and those rims get yanked hard....

Even bolt gun folks need to watch brass after any incident where extraction was difficult or the next time those go through your process they will be different for all those reasons Ned Ludd mentioned.
 
I totally agree with Bugs and RegionRat. When it comes to seating primers consistently the precision primer gauge from Accuracy One is the greatest thing since sliced bread. First I uniform my pockets to a consistent depth indexed off the case head. Then I seat my primers with a Lee ACP bench priming tool that also indexes off the case head. The Lee ACP auto case feed sucks and the primer feed could be better but the seating depth consistency is excellent. I’ve been using BR-2 primers and my primer pocket depth is uniformed to 0.128. Based on my on target experience I seat my primers to a depth of .007. The Lee press generally gives me +/- .0005 consistency which is about the limit of what I can reliably measure.
Accuracy One makes some really good measuring tools. I have been using the precision primer gauge and the seating depth comparator. I also just bought their bullet AOL comparator which should save me a lot of time in sorting bullets.
 
Seating primers w/resp to case head is meaningless, and nowhere near best.
I think I get where you are going with that, but calling it meaningless will confuse the beginners unless we explain that view...

Rookies who are starting out should make sure their primers are below flush, which means inspecting against the depth from the case head.

In context of auto and semi auto weapons, getting them below flush is mandatory. Now that the rookies are cared for....

If mikecr is going where I think he is going I will let him explain the nuance of what he means.
 
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Seating primers w/resp to case head is meaningless, and nowhere near best.
Can you help with best practice? Isn't the primer pocket depth based off of the case head and primer dimensions sized to firtthe pocket? If you are resizing the case properly to fit the chamber and headspace to the bolt, what would be the best reference for primer seating depth?
Honest question.
 
Words from the master’ (Bart)


What’s always absent from the video is the target that proves one particular tool or method is better than another.
 
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Nothing against the K&M method, but it doesn't mean that SPC methods can't give the same results with regular tools does it? I am going to play Devil's Advocate here for a minute.

In the labs (and at home), the tool method study results were no different in terms of primer installation crush control.

However there was a possible disadvantage to the K&M tool that isn't mentioned very often. If one tries to capitalize on the individual inspection without the discipline to cull extremes, then the tool produces very wide spreads on seating depths, thus potentially negating the theoretical advantage when the ammo is inspected after the fact.

For this tool to be an advantage, you are moving the inspection process to this tool. So, if we try to feed the tool non-uniformed or screened components, don't we end up with non-uniformed seating depths?

If you then want to double check the ammo after the fact, how do you know if the workmanship is reject or if it was the result of extremes that added up?

If we find a very shallow sample, it is because a shallow pocket and a tall primer went together? Will we re-seat it? If it is very deep, is it a cull?

You could imagine then that if you were being picky, those very shallow or very deep pockets should be culled or corrected. If we do that anyway, then using a regular tool with SPC puts the whole batch in the same place, and, it can be inspected after the fact.

I am only highlighting the potential pitfalls of the K&M, so don't get me wrong, I still own the tool. but will admit I almost never use it since I don't run in the picky mode without screening primers and brass up front.

If you screen the pockets or uniform them, and understand the batch of primers, then regular tools that drive to a controlled depth put you in the same place or better since you don't get alarmed by seating depths after the fact. YMMV
 
I am only highlighting the potential pitfalls of the K&M, so don't get me wrong, I still own the tool. but will admit I almost never use it since I don't run in the picky mode without screening primers and brass up front.

If you screen the pockets or uniform them, and understand the batch of primers, then regular tools that drive to a controlled depth put you in the same place or better since you don't get alarmed by seating depths after the fact. YMMV
My priority is primer condition w/resp to it's initiating.
NOT how the primer rests w/resp to case head.

I care little if the primer sets 9thou, or 12thou beneath case head (for example), provided the primer is pre-sensitized per my setting. I set uniform pocket depths, my headspace is 1-1.5thou, but I do not group primers by height, or rims by thickness. I let the K&M account for these variances per design.
If I didn't have the K&M, I would measure every rim, and every primer & pocket, and then one of the click adjustable seaters would work for this.

The only time I work with seated primer per case head, is for storage ammo.
For loaded ammo near 6 months stored, and to continue, I'll recover seat the primers 1thou.
This accounts for spring back over time, and they'll never need it again.
 
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K&M makes some really good stuff, I've been using use their dial indicator arbor press to seat my bullets for years and also their neck chamfer tool. Their dial indicator hand priming tool looks like a great idea however it involves way too many steps and individual primer handling for me. I also moved away from hand held primer tools due to my tired old hands, especially when doing a lot of cases. With all of this stuff you tend to run into diminishing returns. I index off the case head for, pocket uniforming, measuring and seating. As long as I can seat primers fairly rapidly and get consistent seating depth I'm happy. As far as how deep to seat the primer below flush with the case head it depends on primer pocket depth and what crush a particular primer “likes”. The only way to tell that is to shoot and “see what the target says”. There are a lot more important factors that effect my group size than a .001 difference in primer seating depth, not the least of which is the “nut that holds the trigger”. When all is said and done the most important factor in winning matches is making the least amount of mistakes.
 
Has anyone actually tried to crush/sensitize a primer anvil by hand ? It’s not as easy as some people might think. Try placing a primer in the jaws of a caliper and squeeze on the anvil as hard as you can to alter the caliper reading.
 
Has anyone actually tried to crush/sensitize a primer anvil by hand ? It’s not as easy as some people might think. Try placing a primer in the jaws of a caliper and squeeze on the anvil as hard as you can to alter the caliper reading.
There tough little sum-of-bucks the way I have had to push on them to get in a tight pocket with the bench primer. I even put one in sideways one time and it didn’t go off.
 
Has anyone actually tried to crush/sensitize a primer anvil by hand ? It’s not as easy as some people might think. Try placing a primer in the jaws of a caliper and squeeze on the anvil as hard as you can to alter the caliper reading.
even if you dont ignite it and injure yourself sounds like a great way to ruin the accuracy on a set of calipers
 

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