Major Factor in Primer Seating Depth Variability
- Thread starter Bryan Z.
- Start date
Why not get a little deeper into this rabbit hole and uniform primer pockets since you're going thru all the trouble measuring and eliminating cases that are out of spec, it might make your primer seating depth more consistent, It's a simple task and you do it only once, 21st Century adjustable tool makes it easy and you can clean primer pockets using the same tool if you'd like.
Ranger188
Silver $$ Contributor
Correct me if I'm wrong, but if you use a primer pocket uniformer, shouldn't the depth
be all the same since it's indexing off the base of the case?
And if you use a primer seater that has a stop, shouldn't the primers all be seated
the same depth? ( other than the difference of the primer height, which isn't going to vary more than .001 )
be all the same since it's indexing off the base of the case?
And if you use a primer seater that has a stop, shouldn't the primers all be seated
the same depth? ( other than the difference of the primer height, which isn't going to vary more than .001 )
The case is lifted when seating within the primer shell holder. Rim thickness affects clearance for lift.
That could wiggle results around.
Ranger188
Silver $$ Contributor
If you eliminate the case from lifting, then primer depth should be consistent.
Simply measure the cups with the anvil removed. I've found those dimensions pretty consistent, so if I want to compare one lot to another, I don't have to measure many.
As far as I know, all priming systems hold cases by their rims.
If the rims are different thickness, then cases will be held in different positions during seating.
To seat to same preload:
The total primer height has to be accounted for.
The rim thickness has to be accounted for.
The pocket depth has to be accounted for.
All at once.
This is not averages or generalizations. You either set same preload or you don't.
Ranger188
Silver $$ Contributor
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 )
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 )
Yes, it’s an easy modification. F class John describes it well in his YouTube vids on the Lee ACP. I did what he said and I get barely any variance in seating depths.
That's what's great about the Lee Acp...It doesn't use a shell holder, it holds it down from inside the case with a plunger type thing. It goes in through the neck and presses the case down.
Well then you have web thickness variance,, likely worse than rim variance..
Not even close to being worse than rim variances. I use the Lee Acp and my results are very similar to the OP's. My primers are always within .0005 variance.
I have a forster bench primer that uses a shell holder and it can vary by as much as .003, even with a hard stop.
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