Primer seating depths

[John Weigel]

I would add to above post that I uniform pockets, and agree with an earlier post that by using an upright bench top tool such as K and M, it is a joy to include it in brass prep routine, and that the brass does indeed slowly flow at back end of case, such that you'll continue to get tiny bit of brass removal on every cycle. It is why I occasionally recheck primer seating for best ignition. Also, I sort primers by weight. My testing that was presented in my post last year clearly showed that a) primer cup and anvil weights are astoundingly constant, yet b) the remaining materials, that include explosive charge vary by well over 50%. Not only are muzzle velocities affected by the variance, but I found that results on paper vary slightly with sorted primers of widely different weight classes. Even if one were to dismiss the general principal of weight sorting primers, its worth remembering that in a brick of CCI BR2s and Federal 210Ms I have found regularly that a dozen or so total EXTREME outliers both light and heavy, await the unwary shooter, possibly accounting for a proportion of mysterious fliers. The load in above target is with primers weighing 5.32 grams, give or take .01 gm - about the middle of the size class distribution, divided by .02 increments.

[PeteFox]

So just to add a bit more information to the topic..

When I'm seating primers I accept a round that is within 0.001 of my target, so if I'm aiming for .006" primer depth , I accept 0.005" > 0.007". That may not be good practice or good enough, but what I'm trying to do is eliminate outliers, not get benchrest level precision.
Each round is measured with an . It will measure both pocket depth and seating depth.

I'm preparing a new lot of 284 Lapua brass - 200 rounds. I decided to measure the primer pockets of large sample to see if anything could be gained by reaming them to a constant depth, given the 0.002" window I use. So I measured 67, a third of them. with this tool it is pretty quick, about 15 mins for the sample. The results are below
Primer Pocket Depth1.jpg.

so I have 66 of the 67 cases within my tolerance range. I think that's pretty remarkable precision for a mass produced item.
The breakdown is in the image below
Primer Pocket Depth2.jpg

All depths except one were within the 0.002" window. So I'm thinking:
- cutting all those pockets is too much work, so I'm not doing it (yet)
- I'll now measure the rest and discard the outliers. If there are too many outliers I'll cut the pockets but if it is around the expected three, I'lll discard
- I'll load the primers and record the primer seating depths and compare

The risk is that I'm stacking tolerances, i.e. primer tolerance on top of pocket depth tolerance, but we'll see.
Pete

[scott/r]

[PaulT35]

I have been using the precision primer seater with micrometer adjustment.
It allows perfect seating to 1/1000.
I have some units for sale with or without primer tubes.
PM if interested

[Tim N]

If you want to be exact with primer crush the K&M seater measures the primer height and depth to primer pocket each time and pick your preferred crush
I use this for team events
Otherwise I use my old Lee hand primer with tray for speedy priming
I can’t tell the difference

[cheech]