Primer seating depth and primer seating force

[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?

 

[jelenko]

Just my perspective.
For benchrest competition winning/losing is separated by hundredths of an MOA => competitors dig to find anything that will make a difference - and, the hunt goes on because the other competitors also keep digging.

 

[Doom]

Just my perspective.
For benchrest competition winning/losing is separated by hundredths of an MOA => competitors dig to find anything that will make a difference - and, the hunt goes on because the other competitors also keep digging.

And most of what they find is anecdotal at best.

 

[Dusty Stevens]

And most of what they find is anecdotal at best.

May be but the scientists are always behind the testers on the match results sheet

 

[cwebster]

My dad called it straining for nats and swallowing flies, but if it makes you fell good, go for it.

 

[Bill Norris]

The "rabbit hole" becomes evidently deeper towards the end of the video IMO when Greg plainly states when the firing pin strikes the primer it drives the primer forward within the pocket which destroys any place of assignment by any gauge. Seat the primer to the bottom of the pocket and go shoot. Testing to some degree is needed for accuracy but once we see diminishing returns it's time to move on. Until my rifles won't show me 1/4 " groups @ 100 yards with the practices I'm using I'll stick with the Lee bench primer. Simply put that will satisfy my accuracy needs forever and out to any distance I would ever get a chance to shoot.

 

[Doom]

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.

Dusty,

I’ve read your carb analogy before and it has no merit in relation to how a cartridge works. But let’s not argue that. You are certainly correct in your comment concerning neck tension and vibration. You have proposed the idea that primer seating may have an effect on SD and accuracy. Let’s consider a properly seated primer (primer wall in contact with the bottom of the pocket) doesn’t move in the pocket when struck by the firing pin. If it does then primer pocket friction and diameter come into to play. Adding additional crush simply reduces the clearance between the anvil and top of the primer. We do not know the actual tolerances on anvil height or the specific hardness of each individual primer, both of which have an impact on lock time. If we assume that the primer doesn’t fire until the cartridge seats on the shoulder then the combustion process begins. If it fires before seating then chamber and case friction and brass dimensions come into play.

These are random sources of error and some are likely to be on the order of the variable in question. Until someone performs enough testing to show consistent results through multiple tests that show predictable correlation between seating depth and ES the results of any test are anecdotal. If you can consistently shoot the difference over multiple shooters then you may have something.

 

[Dusty Stevens]

Dusty,

I’ve read your carb analogy before and it has no merit in relation to how a cartridge works. But let’s not argue that. You are certainly correct in your comment concerning neck tension and vibration. You have proposed the idea that primer seating may have an effect on SD and accuracy. Let’s consider a properly seated primer (primer wall in contact with the bottom of the pocket) doesn’t move in the pocket when struck by the firing pin. If it does then primer pocket friction and diameter come into to play. Adding additional crush simply reduces the clearance between the anvil and top of the primer. We do not know the actual tolerances on anvil height or the specific hardness of each individual primer, both of which have an impact on lock time. If we assume that the primer doesn’t fire until the cartridge seats on the shoulder then the combustion process begins. If it fires before seating then chamber and case friction and brass dimensions come into play.

These are random sources of error and some are likely to be on the order of the variable in question. Until someone performs enough testing to show consistent results through multiple tests that show predictable correlation between seating depth and ES the results of any test are anecdotal. If you can consistently shoot the difference over multiple shooters then you may have something.

You ever tuned a carb? Get that air fuel ratio juuuust right? You ever been on the firing line with some finely tuned br rifles shooting in the ones? You can walk down the line and hear the difference in a tuned powder charge and a not so tuned one just like you can on a carb. Im as scientific as they get- my whole career has been that way, but i learned a long time ago freshly out of school that you just cant apply it to shooting with all the variables involved. Just the ones you added to mine make it a monstrosity. What happens when a bullet slides thru a copper or powder fouled barrel all the while passing a hard spot? Too many variables to even consider, its best to just go see for yourself what changes you can control do when you change them and add that to the memory bank

 

[Doom]

You ever tuned a carb? Get that air fuel ratio juuuust right? You ever been on the firing line with some finely tuned br rifles shooting in the ones? You can walk down the line and hear the difference in a tuned powder charge and a not so tuned one just like you can on a carb. Im as scientific as they get- my whole career has been that way, but i learned a long time ago freshly out of school that you just cant apply it to shooting with all the variables involved. Just the ones you added to mine make it a monstrosity. What happens when a bullet slides thru a copper or powder fouled barrel all the while passing a hard spot? Too many variables to even consider, its best to just go see for yourself what changes you can control do when you change them and add that to the memory bank

Stromberg, Mikuni, Rochester, Carter, Holley, Triumph Spitfires to 396 Chevelle, 383 Road Runners to 440 Chargers, with some Ramblers, Falcons, and LTD’s thrown in.

 

[Dusty Stevens]

Stromberg, Mikuni, Rochester, Carter, Holley, Triumph Spitfires to 396 Chevelle, 383 Road Runners to 440 Chargers, with some Ramblers, Falcons, and LTD’s thrown in.

Im more of an s&s, mikuni, lectron type tuner myself.

 

[J.d. Popkes]

 

[calgarycanada]

Isn’t it great when two experts are on the opposite end of the scale as to what works good lol!
So is one thou crush better than nine thou or other way around?
Luckily I personally don’t have to worry coz I shoot off of elbows.

 

[Straightshooter1]

That's a really nice test approach! However, I can't really draw any conclusions from it unless the very same test is done again at least one more time where the results can be compared.

 

[Webster]

I would say that you seem to be one of those that have a predilection for making things more complicated than they have to be. People who shoot better than you or I will ever shoot simply squeeze the handle until they feel it firmly stop. Why are you trying to make a simple thing complicated? Do you own a set of wind flags or tune loading at the range?

115 replies on 20 days. If anyone really knows the correct answer one reply is all that's needed. If you do a search for primer seating you will find at least 5000 replies.

 

[calgarycanada]

That's a really nice test approach! However, I can't really draw any conclusions from it unless the very same test is done again at least one more time where the results can be compared.

He did do another test with 450 primers and apparently 9 thou crush was still the best.

 

[Straightshooter1]

He did do another test with 450 primers and apparently 9 thou crush was still the best.

Yeah, I'm aware. But the way to be able to draw a valid conclusion about seating depth is to repeat the test keeping things the same. If one wants to see what the difference might be between one set of primers and another (like CCR BR4's vs CCO 450's), then that's OK . . . but it's not a good way to test "seating depth" cause and effect.

 

[JFrank]

I heard him say .009 thousand below the face of the primer pocket which is different than .009 crush after contact with the base of the primer pocket.
My take away is that he tested for himself and found what his platform preferred, my results may vary or perhaps I concur but only a bit of testing will answer that.

 

[WSnyder]

I heard him say .009 thousand below the face of the primer pocket which is different than .009 crush after contact with the base of the primer pocket.

*At ~14:50 he mentions if you have uniformed your pockets (which may now vary from his and SAAMI dimensions) you want to focus on achieving ~.009"anvil crush not necessarily the .009" seating depth in his test (in which he achieved the .009" crush).

EDIT: If it wasn't clear before all of the below is credited to Witch Doctor and are his words. You can find it in the text below the video when you open the video on youtube to view. The attached photo is a screenshot of his drawing showing the dimensions he was working with. Hopefully it make it a bit clearer.

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.

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.

 

[Mulligan]

How about a Macallan 18?

I have to admit, I am completely ignorant about MacAllan 18.
I looked it up, now I'm curious.

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But not THAT curious!

CW