Understanding Primer Seating Depth, How much "crush" is good.

[TheCZKid]

I was getting ready to prime about 1000 pieces of 20 Vartarg, so I can load a bunch up for spring, and making the sage rats fly! But in the past, I have always just seated primers flush with the case head, because that's what my RCBS Universal Priming tool does. I have since purchased a Frankford Arsenal primer seating tool, which is adjustable in .001 increments of seating depth.

I know this topic has been done here, as I've read the posts, so I'm sorry it's a bit redundant.

But then I thought, my primer seating depth is something I need verify before seating all those primers. I know the best answer is going to come down to this: load some test rounds, at different primer seating depths, and to test them. However, there's snow on the ground now here, and I'm not sure I can do that until spring, and I'd like to load a bunch of ammo before spring. So, I thought I'd verify what I "think" I have learned, and see what others have to say.

I've read as many posts on here as I could find, and also watched some good YouTube from Keith Glasscock and Bryan Zolnikov

In Bryan's video he says his .009 test was the best "crush" depth.

So, here's my thinking for solving the problem, first defining the parameters. This is new to me, so I want to make sure.

My understanding of "primer crush" measurement is how much a primers anvil is pushed into the primer cup, after the anvil makes contact with the bottom of the primer pocket.

If a primer is seated to a depth, so the anvil just touches to bottom of the pocket, but is not compressed into the cup, it's 0 crush. Any extra seating depth from there is the amount of "crush" I'm putting on the primer anvil.

I uniformed my primer pockets on my brass with a K&M small rifle primer pocket correction tool.
I measured the depth of the pockets
I took my CCI-400 primers & measured overall height, from cup bottom to anvil top
I measured the cup height alone, giving me the average height the anvil sticks out over the cup, to determine anvil "crush"

Below is my chart I made for myself, to determine how many thousandths deep the bottom of the primer would need to be seated, to have the primer anvil crushed in to the cup by 8 thousandths, just for example. I can adjust that number and the resultant seating depth to correlate to various amounts of crush intended.

Primer Seating: Anvil Crush 5.55 LC cases 20 Vartarg
Average Depth	Average	CCI 400	CCI 400	Rem 7 1/2	Rem 7 1/2
Primer Pockets	Depth	Anvil Height	Cup Height	Anvil Height	Cup Height
K&M Uniformed Pocket	0.1220​	0.1188​	0.1065​	0.1228​	0.1101​
SAAMI Spec .0080		-0.0080​		-0.0080​
Compressed Height		0.1108​		0.1148​
Minus Pocket Depth		-0.1220​		-0.1208​
Thousands Below Head (for .008 crush)		-0.0112​		-0.0060​
Non-uniformed	0.1178​
K&M Uniformer Depth	0.1220​

 

[BoydAllen]

FYI when I talked to a technician at CCI, he told me that their version of proper seating is when the bottoms of the anvil legs are flush with the cup. Do you think that this can be accomplished without the cup touching the bottom of the pocket? Where did you come up with that being incorrect? BTW guys that shoot better than you or I pretty much all seat by feel. I feel it bottom and add a good squeeze.

 

[TheCZKid]

FYI when I talked to a technician at CCI, he told me that their version of proper seating is when the bottoms of the anvil legs are flush with the cup. Do you think that this can be accomplished without the cup touching the bottom of the pocket? Where did you come up with that being incorrect? BTW guys that shoot better than you or I pretty much all seat by feel. I feel it bottom and add a good squeeze.

Hey Boyd.

Yes, the primer height overall is the cup height, plus the extra amount the anvil sticks out of the cup.

So yes, if the anvil just touches the bottom, there's still the amount it was raised above the surface of the cup. In the case of the CCI-400 the cup and anvil height are .1188, the cup itself is .1065. So the anvil sticks out .0123 above the bottom of the cup.

If the anvil just touches to bottom of the primer pocket, like you said the CCI tech instructed, then there would still be another .0123 to push it in before the cup bottomed out.

The reason I'm posting is to verify what people who shoot better than me, like Keith Glasscock and Bryan Zolnikov, both competitive shooters, say about choosing proper primer crush. Neither of those guys say to seat so the primer anvil just touches. I haven't called and talked to CCI, so I'll take your word for it that the technician told you what you said.

I've read the posts here, along with the posts to seat by feel. Unfortunately, my RCBS primer tool (which I've used for years) seated one depth, flush. I see people say to seat .004 below the case head, and so on, but most refer to the amount of "primer crush" which is what I'm trying to verify I that I understand the concept.

Keith Glasscock, YouTube Winning in the Wind, video about how much seating depth is right. He does not seat by feel, neither does F-class John

 

[TheCZKid]

Okay, I just called CCI myself and talked to a technician. He said they always recommend seating the primers between .005 and .008 below the case head. Or if by feel, seat until it stops, then apply a bit more pressure to push the anvil into the cup.

He recommended NOT using a primer pocket uniformer (too late!), because people cant it and gouge the sides of the pocket wall, and that causes misfires and other issues.
And he said, if you are using Lapua or Norma brass, seat .008 to .011 below the case head, as they are not made to SAAMI specs but another, which I can't remember... European.

I assume my Lake City, that I did uniform already, would be the same as Lapua or Norma depth now, because I cut the pockets slightly deeper. So my guessed seating depth would be .008 to .011, like my chart showed.

 

[Pete Wass]

This falls in the category of useless things to worry about along with weighing cases and bullets, primers too. What maters most is what's inside the cases. and precise loading.

 

[Eagle Six]

This does not address your question of crush. However, I have read your entire thread and offer my opinion, which you didn't ask for. If it were me I would not play around with crush to load a 1,000 rounds for the forth coming season unless I could test a small batch to confirm. Without that test, I would set up my new priming tool to duplicate the RCBS press, or revert back to the press. I would then be ready for the season with a known load and could experiment with crush when time permitted. I know, not much help, just had to run my mouth.

 

[M-61]

I seat the primers until they bottom in the clean primer pocket. Not drilled, reamed, nothing. Just cleaned. Seated. Done.
Has worked successfully for me since 1963.
Am I a champion shooter? Nope.
Pretty tight groups though with a few different BR rifles.

 

[JFrank]

@TheCZKid
Don’t let a little snow stop you from putting out a piece of paper and do a little testing. Normally I get the range all to myself on snowy days.

 

[SSL]

FYI when I talked to a technician at CCI, he told me that their version of proper seating is when the bottoms of the anvil legs are flush with the cup. Do you think that this can be accomplished without the cup touching the bottom of the pocket? Where did you come up with that being incorrect? BTW guys that shoot better than you or I pretty much all seat by feel. I feel it bottom and add a good squeeze.

Yep...bottom out and then a bump. Not real scientific, but it works for me.

 

[TheCZKid]

I agree with Eagle Six (opinion appreciated), my test loads have all been flush with the case-head, from the RCBS Universal seater. And unless I can do some testing, I'll stick with that. I think I might be able to go shoot Sunday or Monday, as the temps might be a high of about 50, so that would be my window.

My motive for the post was to be sure I knew more clearly about primer seating. It was not on my radar until recently. But the idea of prepping my brass with primers got me to thinking, might as well seat them all the best I can.

So, I'll try to do some test shots with my best loads and pick 3 or 4 seating depths. Like flush, .004, .008 .011 and see what, if anything, they tell me.

 

[Eagle Six]

I will be interested in your test results when you have some data, soon or in the future. I'm currently using an RCBS priming tool, seat then bump it a little by feel.

 

[TheCZKid]

I think my RCBS Universal has maybe slight gotten worn over time. It's got the spring loaded jaws on the sides, which accepts a wide range of brass diameters. Its max seating is now flush, but I think it used to allow a little more when I first got it. Thus the reason I got the Frankford Arsenal with thousandths depth dial.

 

[Eagle Six]

Over the years I have wore out three of those universal hand tools and broke two levers. I'm now using the automatic tool and have been used to priming in a standing position which seems to provide me with uniform bump pressure (for a better term!). Someone makes a micro adjustable gizmo for seating death for that tool, but as yet I haven't considered getting it. Maybe I should think about that more.

 

[BoydAllen]

I agree with Eagle Six (opinion appreciated), my test loads have all been flush with the case-head, from the RCBS Universal seater. And unless I can do some testing, I'll stick with that. I think I might be able to go shoot Sunday or Monday, as the temps might be a high of about 50, so that would be my window.

My motive for the post was to be sure I knew more clearly about primer seating. It was not on my radar until recently. But the idea of prepping my brass with primers got me to thinking, might as well seat them all the best I can.

So, I'll try to do some test shots with my best loads and pick 3 or 4 seating depths. Like flush, .004, .008 .011 and see what, if anything, they tell me.

Bart Sauter was on the winning US team for the World Benchrest Championship. He has a range that shoots out of his basement from a concrete bench down a very narrow slot, and his testing, using his rail gun showed that as long as the primers were bottomed they shot fine, which is definitely quite a bit deeper than flush. Seating Federal primers the way I do in Lapua 6BR brass, I measured the depth of a few primers that were seated with a little compression past touch and they were all pretty close to .009 deep. FYI virtually no one that is in thee primer business, or is a top shooter recommends seating flush.

 

[BoydAllen]

Hey Boyd.

Yes, the primer height overall is the cup height, plus the extra amount the anvil sticks out of the cup.

So yes, if the anvil just touches the bottom, there's still the amount it was raised above the surface of the cup. In the case of the CCI-400 the cup and anvil height are .1188, the cup itself is .1065. So the anvil sticks out .0123 above the bottom of the cup.

If the anvil just touches to bottom of the primer pocket, like you said the CCI tech instructed, then there would still be another .0123 to push it in before the cup bottomed out.

The reason I'm posting is to verify what people who shoot better than me, like Keith Glasscock and Bryan Zolnikov, both competitive shooters, say about choosing proper primer crush. Neither of those guys say to seat so the primer anvil just touches. I haven't called and talked to CCI, so I'll take your word for it that the technician told you what you said.

I've read the posts here, along with the posts to seat by feel. Unfortunately, my RCBS primer tool (which I've used for years) seated one depth, flush. I see people say to seat .004 below the case head, and so on, but most refer to the amount of "primer crush" which is what I'm trying to verify I that I understand the concept.

Keith Glasscock, YouTube Winning in the Wind, video about how much seating depth is right. He does not seat by feel, neither does F-class John

Reread what I wrote. He said seated so that the bottoms of the anvil feet are flush with the cup. The bottoms of the feet.

 

[Straightshooter1]

I was getting ready to prime about 1000 pieces of 20 Vartarg, so I can load a bunch up for spring, and making the sage rats fly! But in the past, I have always just seated primers flush with the case head, because that's what my RCBS Universal Priming tool does. I have since purchased a Frankford Arsenal primer seating tool, which is adjustable in .001 increments of seating depth.

I know this topic has been done here, as I've read the posts, so I'm sorry it's a bit redundant.

But then I thought, my primer seating depth is something I need verify before seating all those primers. I know the best answer is going to come down to this: load some test rounds, at different primer seating depths, and to test them. However, there's snow on the ground now here, and I'm not sure I can do that until spring, and I'd like to load a bunch of ammo before spring. So, I thought I'd verify what I "think" I have learned, and see what others have to say.

I've read as many posts on here as I could find, and also watched some good YouTube from Keith Glasscock and Bryan Zolnikov

In Bryan's video he says his .009 test was the best "crush" depth.

So, here's my thinking for solving the problem, first defining the parameters. This is new to me, so I want to make sure.

My understanding of "primer crush" measurement is how much a primers anvil is pushed into the primer cup, after the anvil makes contact with the bottom of the primer pocket.

If a primer is seated to a depth, so the anvil just touches to bottom of the pocket, but is not compressed into the cup, it's 0 crush. Any extra seating depth from there is the amount of "crush" I'm putting on the primer anvil.

I uniformed my primer pockets on my brass with a K&M small rifle primer pocket correction tool.
I measured the depth of the pockets
I took my CCI-400 primers & measured overall height, from cup bottom to anvil top
I measured the cup height alone, giving me the average height the anvil sticks out over the cup, to determine anvil "crush"

Below is my chart I made for myself, to determine how many thousandths deep the bottom of the primer would need to be seated, to have the primer anvil crushed in to the cup by 8 thousandths, just for example. I can adjust that number and the resultant seating depth to correlate to various amounts of crush intended.

Primer Seating: Anvil Crush 5.55 LC cases 20 Vartarg
Average Depth	Average	CCI 400	CCI 400	Rem 7 1/2	Rem 7 1/2
Primer Pockets	Depth	Anvil Height	Cup Height	Anvil Height	Cup Height
K&M Uniformed Pocket	0.1220​	0.1188​	0.1065​	0.1228​	0.1101​
SAAMI Spec .0080		-0.0080​		-0.0080​
Compressed Height		0.1108​		0.1148​
Minus Pocket Depth		-0.1220​		-0.1208​
Thousands Below Head (for .008 crush)		-0.0112​		-0.0060​
Non-uniformed	0.1178​
K&M Uniformer Depth	0.1220​

View attachment 1516265

You're data matched my data very well. A few months ago I did the same kind of measuring as you've shown. I also measure CCI-400's and measured some of my Federal 205M's. Likewise, I've uniformed my Lapua .308 cases to a depth of .1220", but with my 21th Century primer pocket uniformer; this number being the minimum to get all the pockets to a uniform depth. Both my 400's and 205M's measure .118 to .120" (the large majority being .118-.119"). As I recall, my CCI primer cup height (with anvil) was ~.108"

For those primers that measure .118", seating them to .004 below flush meant the anvil was just touching and to get the .004 crush I would have to seat them to .008. In the past I has been seating them to ~.005 below flush, so was not getting as much crush as I though I was getting. The last batch I fired, I had seated them to that .008-.009" and the cartridges performed quite well. I was a little concerned that the firing pin wouldn't deliver enough energy, especially in cooler temperature I fired them in (only the low 50°F, cold for us in the lower desert of AZ ).

For me, the exercise was simply to get a better visual picture of what I was actually doing when seating my primers. With variations in case primer pocket depths as well as the primer heights, it helps to know what's actually going on in this regard. It's just the way I'm wired, I guess.

 

[gunsandgunsmithing]

Feel is the best way, IMHO. Ya gotta be able to shoot any difference that may well not be there at all. I think this is a topic that has just gone too far with over thinking. I know, there are people who are just wired differently and feel is greek...a foreign language. But at some point, one has to have just a wee bit of that wiring or find a different hobby if everything has to be quantified to the inth degree for it to work. I've never used any sort of guage for this and if it gets to the point where I'm losing because of that, I'll take up brain surgery or something simple.

 

[K22]

As William Shakespeare once said, "this is much to do about nothing" or some such thing.

Of all the numerous variables involved with results on target, I submit this is the least significant, if significant at all. But hey, if you like experimenting, testing, and using your components do such things then go for it. After all it's supposed to be a hobby - different strokes for different folks.

Seating your primers by feel to the bottom of the pocket is intuitively the obvious best approach, at least to me, because then the variation in primer pocket depth, even those uniformed becomes a non-issue. If you start messing around with not seating them to the bottom of the primer pocket, then you expose yourself to misfires. Reliability is just as important as precision, at least to me.

 

[D Coots]

How much crush does a sage rat like?

 

[TheCZKid]

Sage rats prefer .008, but that was a very small data sample, and right before they performed Rat-O-Batics!