Primer Seating Depth, How Much Do You Care?

[Killick]

Also, do you sort for depth?

 

[Kracken McGraw]

Bottom them out for a slight crush on the RCBS bench mounted tool.

 

[wkdickinson]

Bottom them out for a slight crush on the RCBS bench mounted tool.

Same here, except I use the Lee bench too.

 

[SSL]

I use an RCBS hand tool. Feel the primer bottom out and then give it a little "nudge". Run finger over it to feel a slight indentation.

 

[mikecr]

2-5thou crush

 

[243winxb]

RCBS Ram Prime - I do a "drop test" while seating the primer. This tells me that the pocket has not expanded to much.
Then light crush fit.

The primer can be any where from flush to .008" below the case head. (SAAMI)

If you want perfection, uniform the depth of the pockets.

 

[J.d. Popkes]

Just beginning to test this. Use primal rights tool. Measure with accuracy one tool. Only thing I can verify for sure is, hand primer by feel I cannot get consistent depths. I can with primal rights tool. How much it matters, for me, Is yet to be determined. Some better shooters than me on here that said/showed it matters. We’ll see?

 

[fkimble@charter.net]

If you don't uniform the primer pockets, then you probably won't get a consistent depth by feel. My 200 yd XTC ammo only gets a trip thru the Dillion Super Swage (once fired LC brass) and the Gracy trimmer. My 300 and 600 get pockets uniformed, flash hole uniformed and deburred and a trip thru the Gracy and the Super Swage. The 200, 300 and 600 cases become practice brass after a few firings. Never measured a primer depth and have never had a primer fail to fire due to seating issues.

Frank

 

[J.d. Popkes]

If you don't uniform the primer pockets, then you probably won't get a consistent depth by feel. My 200 yd XTC ammo only gets a trip thru the Dillion Super Swage (once fired LC brass) and the Gracy trimmer. My 300 and 600 get pockets uniformed, flash hole uniformed and deburred and a trip thru the Gracy and the Super Swage. The 200, 300 and 600 cases become practice brass after a few firings. Never measured a primer depth and have never had a primer fail to fire due to seating issues.

Frank

I use k&m uniformers.

 

[INTJ]

Measuring the depth a has primer seated, and even sorting by this seating depths, doesn't do much. Primers should be seated to a consistent crush. Since primer cup heights vary and even uniformed pockets vary, seating to a consistent depth doesn't mean much when it comes to getting a consistent crush.

You can get close by feel with a quality primer seating tool, but the gold standard is to use the K&M Primer gauge. This tool measures the pocket depth of the exact case and the cup height of the exact primer you are about to seat, which allows you to see the exact amount of crush.

 

[J.d. Popkes]

Measuring the depth a has primer seated, and even sorting by this seating depths, doesn't do much. Primers should be seated to a consistent crush. Since primer cup heights vary and even uniformed pockets vary, seating to a consistent depth doesn't mean much when it comes to getting a consistent crush.

You can get close by feel with a quality primer seating tool, but the gold standard is to use the K&M Primer gauge. This tool measures the pocket depth of the exact case and the cup height of the exact primer you are about to seat, which allows you to see the exact amount of crush.

At any distance?

 

[INTJ]

At any distance?

The general rule of thumb is .002" crush for a small rifle primer and .003" for a large rifle primer. Of course, that can be adjusted anywhere up to about .005" for fine tuning.

Guys get really close with feel alone.

 

[J.d. Popkes]

The general rule of thumb is .002" crush for a small rifle primer and .003" for a large rifle primer. Of course, that can be adjusted anywhere up to about .005" for fine tuning.

Guys get really close with feel alone.

I mean, are you saying that primer seating depth doesn’t matter, at any range or distance. I’m assuming some things are less important at a couple hundred yards.

 

[INTJ]

I mean, are you saying that primer seating depth doesn’t matter, at any range or distance. I’m assuming some things are less important at a couple hundred yards.

I am saying that measuring primer seating depth isn't the right measurement. Primer crush is the right measurement, and there is little correlation between primer crush and primer seating depth. We may think that we have achieved consistency in primer seating when measuring seated primer depth, but we haven't. Uniformed primer pockets have variation, and primer cup heights have even more variation.

I used to seat the primers for my 1000 yd BR rifle by feel, measure the seating depths, try to fix the shallow ones, and then sort them into groups based on the measured seating depth. This was with primers that were weight sorted. The ES of my best loads was in the mid teens with my 6 BRAI.

Then I started using a K&M Primer Gauge. This tool measures the depth of the pocket and the height of the primer cup of the exact primer and case being seated. The ES of my best loads dropped to the high single digits.

Now I don't obsess about ES, I obsess about group size. However, ES is an indicator of the quality and consistency of our loading practices. While primer seating isn't all of the equation, I did shoot four IBS 1000 yd screamer groups this year, one with my 6 BRA light gun and three with my 300 WSM heavy gun.

None of this level of primer precision is not needed outside of LR BR and maybe ELR. For most disciplines, simply seating the primer until you feel it bottom out and then squeezing it a bit more works extremely well. And if you have a good enough tool and feel, this method works well in LR BR as well.

So just because all the primer depths measure .003" doesn't mean that they all have the same amount of crush.

 

[tsyarnall]

If you talk to some, “crush” can be different for the various brands of match primers and I have no reason to doubt them.

 

[J.d. Popkes]

I am saying that measuring primer seating depth isn't the right measurement. Primer crush is the right measurement, and there is little correlation between primer crush and primer seating depth. We may think that we have achieved consistency in primer seating when measuring seated primer depth, but we haven't. Uniformed primer pockets have variation, and primer cup heights have even more variation.

I used to seat the primers for my 1000 yd BR rifle by feel, measure the seating depths, try to fix the shallow ones, and then sort them into groups based on the measured seating depth. This was with primers that were weight sorted. The ES of my best loads was in the mid teens with my 6 BRAI.

Then I started using a K&M Primer Gauge. This tool measures the depth of the pocket and the height of the primer cup of the exact primer and case being seated. The ES of my best loads dropped to the high single digits.

Now I don't obsess about ES, I obsess about group size. However, ES is an indicator of the quality and consistency of our loading practices. While primer seating isn't all of the equation, I did shoot four IBS 1000 yd screamer groups this year, one with my 6 BRA light gun and three with my 300 WSM heavy gun.

None of this level of primer precision is not needed outside of LR BR and maybe ELR. For most disciplines, simply seating the primer until you feel it bottom out and then squeezing it a bit more works extremely well. And if you have a good enough tool and feel, this method works well in LR BR as well.

So just because all the primer depths measure .003" doesn't mean that they all have the same amount of crush.

Yeah, I don’t know, sounds like you have looked into this quite a bit. Good information in your posts. I have pretty good luck getting my pockets identical. I know that primer height varies a tiny bit. I have been seating from touch to different amounts of crush. In my experience measuring the ones I seat by feel they’re way more inconsistent. The accuracy one tool is amazing for measuring everything about primer and pocket. Just another thing for me to try and tune. Or maybe it’s not.

 

[mikecr]

If you talk to some, “crush” can be different for the various brands of match primers and I have no reason to doubt them.

2thou crush works best with Feds, 5thou works best for CCIs. That much I've logged.

 

[NorCalMikie]

Bottom of the primer pocket and a "little more" with a Lee Auto Prime. It'a a feel thing.
You'll know (or find out the hard way) if you get a "high primer" in an M1A or most any gas gun.

 

[INTJ]

Yeah, I don’t know, sounds like you have looked into this quite a bit. Good information in your posts. I have pretty good luck getting my pockets identical. I know that primer height varies a tiny bit. I have been seating from touch to different amounts of crush. In my experience measuring the ones I seat by feel they’re way more inconsistent. The accuracy one tool is amazing for measuring everything about primer and pocket. Just another thing for me to try and tune. Or maybe it’s not.

The total variance in cup depth and primer pockets can be as much as .005." Most if that is variation in cup heights. If all your seated primers measured .003", and there is .005" difference in primer cups and pockets, then the crush is nowhere near being consistent.

I too have the Accuarcy One tool, as well as another custom made primer tool. The only way to get a consistent crush using these tools is to sort all the cases by pocket depth and then measure all the primer cup heights. I no longer use these tools.

This tool fixes all of those issues. It is slower than a typical primer tool, but since you don't have to measure anything after you are finished the total time spent priming is less.

Primer Guage - Hand Priming Tools - K&M Shooting

The Primer Guage employs a dial indicator ensuring that each primer is seated the precise depth required. Learn more about this precise hand primer here.

kmshooting.com

 

[J.d. Popkes]

The total variance in cup depth and primer pockets can be as much as .005." Most if that is variation in cup heights. If all your seated primers measured .003", and there is .005" difference in primer cups and pockets, then the crush is nowhere near being consistent.

I too have the Accuarcy One tool, as well as another custom made primer tool. The only way to get a consistent crush using these tools is to sort all the cases by pocket depth and then measure all the primer cup heights. I no longer use these tools.

This tool fixes all of those issues. It is slower than a typical primer tool, but since you don't have to measure anything after you are finished the total time spent priming is less.

Primer Guage - Hand Priming Tools - K&M Shooting

The Primer Guage employs a dial indicator ensuring that each primer is seated the precise depth required. Learn more about this precise hand primer here.

kmshooting.com

Cool, thanks, sounds good