Primer seating depth testing

[Alex Wheeler]

I have been playing with the Primal Rights CPS primer seating tool. Conditions where not ideal this morning but I wanted to run the test at 1k. Even though the conditions where not very good, in my opinion the results certainly tell me primer seating depth does matter. I shot this with my 6BRA with a BR4 primer. Group size was effected as well as point of impact. Each .002" increment was worth about 1.5-2" in poi. I measured the pocket depth and the primer height to determine the "crush". .004" and .006" overlapped and held 2.7" of vertical for all 6 shots. We will continue to work on this and will share more as we learn it.

 

[Mikecr]

I set CCIs at 5thou crush. Feds and Wins at 2thou.
My testing led to that long ago, using the indicated K&M.

If you want to see another interesting matter of primer results, set them to best crush and adjust firing pin fall.
You'll see grouping open- close- open.
I believe it is this combination leading to the abstract of folks swapping primers for best results.
Different optimum striking for different primers.

I also believe we can use any primer we like, provided we test and set best striking for it, and that this should be done before load development begins(like fire forming and full seating testing).

 

[Alex Wheeler]

Certainly some primers respond to more energy than others. Primer choice for me, has show a potential to give a wider tune. Most of them will shoot small but some will hold tune better. Theres two things to consider, how an ignition works with the primer, and how the primer works with a powder. It does seem like an ignition will pick a primer with a fixed powder, but switch powders and a new primer may win.

 

[Alex Wheeler]

B was .002" crush, 5.882" vertical
R was .004" crush, 2.745" vertical
G was .006" crush, 1.359" vertical
Y was .008" crush, 3.918" vertical
N was .010" crush 4.835" vertical

 

[badthirtyone]

Great data. Thanks for sharing this.

 

[dusty218]

this is a very interesting topic. I'll be very interested to follow your further testing! With that at what distance do you feel that will you be able to see the affect of the seating depth? My load development consists of proper barrel break in then run a ladder find the node then tune bullet seating depth. I have great results with that method and achieve single digit ES & SD. and I'm always looking for more info on further tuning for higher accuracy!

 

[MagnumManiac]

I have the CPS too, but only tested at 600 so far with WLRM and Fed215 with .002", .003" & .004" crush. It only had a swing of 3" vertical, but the Fed215's opened the group in overall size more then the WLRM's did. POI shifted low to high, which surprised me, as my previous testing with the K&M didn't show this.
I just changed firing pin springs, so I guess I'll have to tune again.
Cannot get ANY CCI primers in any flavour at the minute, want to re-visit the BR-2 in my 264WM. Have just got 8lbs of H50BMG to try.

Cheers.

 

[trailrider121]

Excellent testing and data. Thanks for sharing the results with primer seating depth testing.

 

[kiwikid]

Alex will the amount of shoulder bump also affect the results of the primer depth tests? It would seem to me that more shoulder bump would result in less strike energy.

 

[Roninco]

Do you routinely uniform primer pockets for depth or is it case manufacturer dependent?

 

[txsendero]

When you're talking the amount of "crush", is that amount (.006" for example) the amount that the primer is seated below the head of the case?

 

[Rhovee]

You have to measure the thickness of the primer. Then the depth of the primer pocket. Then you will know. Crush is a depth past touching. If your primers measure .124 and your pockets are .126, then .002 below the case head is touching.

 

[trailrider121]

You have to measure the thickness of the primer. Then the depth of the primer pocket. Then you will know. Crush is a depth past touching. If your primers measure .124 and your pockets are .126, then .002 below the case head is touching.

Yep, what Rhovee said is correct.

 

[MagnumManiac]

Actually, that measurement only tells you the difference between a primer and cup that has zero crush.
The measurement you want is the amount of crush AFTER the anvil and cup are flush with each other on the bottom of the pocket. This can be .008" or more.

Cheers.