Major Factor in Primer Seating Depth Variability

[quest450]

Leaving aside the Lee ACP results - they are what they are, and I'm disputing them - does anyone here have any good guesses why the CPS would have so much more variation than the PMA? Given that they both reference off the case rim the same way, and both appear to be pretty solidly made... it seems odd that there was such a difference. I'm not disputing or challenging Bryan's numbers, I'm just trying to make sense of *why*...

operator error or insufficient brass prep would be my guess

 

[memilanuk]

operator error or insufficient brass prep would be my guess

Well, given the same cases were used for all three tools, I think we can rule out the latter.

As for the former... I know that gets thrown around a lot, but seriously how hard is it to pull a lever? How hard *should* it be to get a consistent result when the ram goes to a hard stop? Unless that is the problem - that it's harder to feel that hard stop with the CPS than with the hand-held tools?

 

[quest450]

Well, given the same cases were used for all three tools, I think we can rule out the latter.

As for the former... I know that gets thrown around a lot, but seriously how hard is it to pull a lever? How hard *should* it be to get a consistent result when the ram goes to a hard stop? Unless that is the problem - that it's harder to feel that hard stop with the CPS than with the hand-held tools?

I'm not sure but I'd like to add "an agenda" to my previous reply
And I'd definitely send back the CPS back for troubleshooting

 

[RegionRat]

I have many different priming tools, including the Sinclair, PMA, K&M, CPS, ACP, etc.

I like to run the PMA to hard stop and don't try to go by feel.
My results end up the same as Bryan's conclusions, at best you will only match the rim thickness variation with a rim datum tool driven to a hard stop.

It took me a little while to get my CPS results to the same as the PMA, but they match.

I have heard Greg mention it takes a little break-in to get the CPS to settle, and I tend agree.

 

[stavey]

Still available on ebay. Awfully good deal.

 

[Dos XX]

Was the K & M with dial indicator included in this test? If not, why?

 

[WSnyder]

there was no correlation even with the Lee APC

Thanks. I’m my haste this morning while I was more focused on other things I had forgotten your test used the ACP.

Time to go back, re listen and ponder some more

 

[BoydAllen]

If you watch the video, the Lee ACP doesn't use a shell holder and
won't have the difference in rim thickness as a problem.
If you use the Lee and a primer pocket uniformer, would seem to
fix most of the problems with slack or different primer pocket depths,
since both are indexing off the base of the case and not the rim. ( thickness )

And here it is.

 

[quest450]

sure..... you can put lipstick on a pig

 

[stavey]

I’m guessing there’s a lot of CPS owners wishing they could put some lipstick on their pigs. LOL

 

[jackieschmidt]

What do you do when the primer pockets get so loose in your 6PPC cases that there is practically no inference fit to speak of……..and the things still shoot as good as ever.

Over 20 years ago, Gene Bukys and several of us did some experimenting with primer seating depth and primer pocket uniforming on 6PPC cases made from Lapua 220 Russian.

I would bet shooters like Boyd Allen who have been around a while remembers our write up on Benchrest.com.

He had an adjustable primer seater that allowed you to seat primers from dead flush to a firm bottoming out in the cup.

Using our Rail Guns, we spent a full day playing with different depths, and none of it showed up on the target as long as they were all the same. We came to the conclusion that simply seating the primer to where it was seated on the inside of the pocket was as good as anything.

But keep in mind, we were not worrying about ES or SD, all we were interested in was the agging capability of thr rifle at 200 yards. That being the rifles ability to stack one bullet atop the other.

Maybe federal 205 primers were better 20 years ago.
We also took ten cases that had the pockets uniformed, and ten that didn’t. We mixed them all together and to our surprise, the results did not show up on our targets as long as we seated the primer against the bottom of the pocket.

I made a complete write up on Benchrest.com. Our conclusions were that primer uniformity had a un noticeable affect on the rifles agging capability. Just seat them the same way each time, preferably seated against the bottom of the primer pocket.

I don’t think Gene or I ever “uniformed” a Lapua 220 Russian primer pocket again.

I commend Bryan for his efforts in this. For those that want to worry about this sort of thing, it is great information.

 

[Bryan Z.]

I'm not sure but I'd like to add "an agenda" to my previous reply
And I'd definitely send back the CPS back for troubleshooting

Alright, I’ll admit it…Lee paid me millions to boost their no longer produced product. Bwahahaha! Are you a comedic spoof account or something? Seriously though

 

[BoydAllen]

Jackie, you probably remember this. Sometime back, Bart wrote about seating, tested with his rail gun. His results showed that as long as the primer was touching the bottom of the pocket that the accuracy was good. I have never been as good a shooter as you and Bart are (or Gene was) , but I am smart enough to pay attention when you share the results of a test. I have found by pulling a primer that I had seated with a hand tool with about all the force that I can muster with one hand, that nothing was amiss when I pulled it, unfired, no broken pellet, no flattening of the cup, bottom of anvil feet flush with the cup except for a very slight protrusion of one. You guys have shown that as long as they touch bottom your rail guns cannot tell the difference. I think that that leaves a wide range that will work. I know this drives the seat by depth, and to the same number of thousandths compression guys nuts, but since you all shoot or shot better than they do, I do not loose much sleep over the issue, and as long as the worriers primers touch the bottoms of their collective pockets, I am pretty sure that they will be fine.

 

[Alex Wheeler]

Tom Mousel and myself did some testing on this subject at 1K with our Br rifles. What we both saw was that there is a window of crush that shot better. But its hard to miss that window seating by feel. Also, because we saw that a primer did like that window of crush, not a depth below the case head that means all other variables come into play. My last lot of primers had .008" height variation, ad in rim and pocket variation. So potentially you could end up with .010" difference in crush if you did not sort all of that out and adjust for it. I simply am not willing to do THAT much work. Not to say there would not be some very small gain. That terrible lot of primers also shot me a 1.6" agg at 1k seating by feel, not sorting anything. Normally I would never say thats good enough but in this case it was for me.

 

[6BRA]

Out of my CPS: +/-0.001" is the very best I have been able to achieve using Lapua brass with pockets cut at 0.1315" depth using 21st Century pocket uniformer and using Primal Rights PrimeWhere and AccuracyOne w/ 0.0001" Mitutoyo Absolute Digimatic Indicator. My results align with Bryan's test results. Unless we are both testing w/ CPS units that have internal tolerance issues, I have to assume that people getting better results are using measuring instruments of lower accuracy/resolution or they aren't checking every single primer they seat. If someone is using of equal or greater quality indicators and getting better results than I am showing, please share your results. Attached are photos of my equipment used to cut, measure & seat primers. Primer pocket variation on this batch of 50 (LRP) is +/-0.0002". I would love nothing more than to have my seated primers measure within a +/-0.0005" tolerance. I will post my data log of the measured pockets and primers soon, once I locate them in my files.

The part in Bench Addicts picture that is very visible and takes the CPS to right at $1000.00. is the most important piece of the puzzle if you have a CPS. I too, have everything in his pictures. The advantage over the K&M is you never have to touch a primer. Once pockets are uniformed, the datum is off the bottom of the pocket. Rim thickness and primer thickness don't matter at this point. If you spent this much money on the CPS, you need to continue on. The CPS by itself, while very well made, is not able to get us where we need to be.

 

[BP1]

What do you do when the primer pockets get so loose in your 6PPC cases that there is practically no inference fit to speak of……..and the things still shoot as good as ever.

Over 20 years ago, Gene Bukys and several of us did some experimenting with primer seating depth and primer pocket uniforming on 6PPC cases made from Lapua 220 Russian.

I would bet shooters like Boyd Allen who have been around a while remembers our write up on Benchrest.com.

He had an adjustable primer seater that allowed you to seat primers from dead flush to a firm bottoming out in the cup.

Using our Rail Guns, we spent a full day playing with different depths, and none of it showed up on the target as long as they were all the same. We came to the conclusion that simply seating the primer to where it was seated on the inside of the pocket was as good as anything.

But keep in mind, we were not worrying about ES or SD, all we were interested in was the agging capability of thr rifle at 200 yards. That being the rifles ability to stack one bullet atop the other.

Maybe federal 205 primers were better 20 years ago.
We also took ten cases that had the pockets uniformed, and ten that didn’t. We mixed them all together and to our surprise, the results did not show up on our targets as long as we seated the primer against the bottom of the pocket.

I made a complete write up on Benchrest.com. Our conclusions were that primer uniformity had a un noticeable affect on the rifles agging capability. Just seat them the same way each time, preferably seated against the bottom of the primer pocket.

I don’t think Gene or I ever “uniformed” a Lapua 220 Russian primer pocket again.

I commend Bryan for his efforts in this. For those that want to worry about this sort of thing, it is great information.

Exactly…thank you, I tested some seating from .002-.005 in my 223 at 500meters several times and they shot pretty much the same to where I don’t worry about it anymore.. I use a CPS and a rcbs hand held seater.

 

[memilanuk]

The part in Bench Addicts picture that is very visible and takes the CPS to right at $1000.00. is the most important piece of the puzzle if you have a CPS.

Which part (or parts) would that be?

 

[tovaert]

I mainly shoot service rifle loads (77 gr SMKs) in LC brass. After a slam fire (due to an improperly seated primer), I started uniforming pockets after each firing. I use the Sinclair tool on a small DC motor. I don't take any measurements afterwards, but looking at the pile of residue removed after processing a few hundred rounds, it surprises me how much fresh shaved brass is removed, and it's not from the sides of the pockets.