Thread: Primers, how flat is too flat

Hi all, looking for some advice and sources of information.
how flat is too flat with primers, as an indication of pressure.

I decided to ask more about this after reading another thread on here recently and noticing a couple of flatter than usual primers with what should be a mild load after my last outing.

the 243 is a barnard SM action and i have never had a stiff bolt lift,
load data is
Lapua brass on it's 4th or 5th reload,
CCI 200 large rifle primer.
ELD-M 108gr over 46 gr of RL-26, COL 2.83". Alliant quote a load max for 105gr amax of 46.7gr
75gr HP Hornady /Speer over 44 gr W760, COL 2.64". Hodgdon give a load range of 42-46gr.

The primers used under the W760/H414 were noticeably flatter. See primers 2nd and 3rd from left




Next lot is 358 win shot out of a 1975 Savage 99
Win Brass, CCI 200 primers.
Sierra GK 225gr over 48 gr Varget/2208. Hodgdon give a load range of 45-49gr.
Hdy 158gr XTP over 12 gr Trailboss. Max case volume 14-16 gr based on bullet seating depth

Cases on left had the full power loads, those on the right the trail boss loads.



Thanks all, keen to hear your feed back and comments
Z

Originally Posted by ZQLewis

Hi all, looking for some advice and sources of information.
how flat is too flat with primers, as an indication of pressure.

I decided to ask more about this after reading another thread on here recently and noticing a couple of flatter than usual primers with what should be a mild load after my last outing.

the 243 is a barnard SM action and i have never had a stiff bolt lift,
load data is
Lapua brass on it's 4th or 5th reload,
CCI 200 large rifle primer.
ELD-M 108gr over 46 gr of RL-26, COL 2.83". Alliant quote a load max for 105gr amax of 46.7gr
75gr HP Hornady /Speer over 44 gr W760, COL 2.64". Hodgdon give a load range of 42-46gr.

The primers used under the W760/H414 were noticeably flatter. See primers 2nd and 3rd from left
Attachment 116537
Attachment 116538


Next lot is 358 win shot out of a 1975 Savage 99
Win Brass, CCI 200 primers.
Sierra GK 225gr over 48 gr Varget/2208. Hodgdon give a load range of 45-49gr.
Hdy 158gr XTP over 12 gr Trailboss. Max case volume 14-16 gr based on bullet seating depth

Cases on left had the full power loads, those on the right the trail boss loads.
Attachment 116539
Attachment 116540

Thanks all, keen to hear your feed back and comments
Z

Green holder bottom right would get my attention. I've always had a chrony to refer to when reloading. I suggest you acquire one and build your loads up from mid recommended load in .5 gr increments.

Looking at the pics on my phone. Apart from one on the right in the green box that is sort of close, you don't have any what I would call flat primers that I can see.
No ejector marks or polishing what so ever.
I personally wouldn't worry about those loads till the summer.
Check them on a hot day. You might see a flat primer then

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Thanks outlander, it did get my attention.
I normally start with 0.5 and then .3 gr steps and go 0.5-1 gr over where I settle back on.
That 75 gr load I was being lazy and in a hurry to get something to take way just in case the opportunity to shoot some wallabies came up..
Previous load workups with 58gr vmax, 87gr vld, 105gr vld and the 108gr eldm suggested I was all ok up to or a little over book max so this time I just went straight to middle of the load range.
P's I do have a cheap cronie but had loaned it out.
Z

The pressures are fine but you have a problem with the nose of your firing pin. The nose should be a true hemisphere and not have a step in it which can sometimes cause ruptured primers.

I can see an ejector mark on that bottom right

Yes nice and flat right to the edge, yet his mate on the left is rounded. How come the difference

Pressure looks ok to me. Primers are still quite round and there is not much in the way of brass flow/ ejector swipe marks.
I agree with Gundoc, the primer strikes look odd to me. Im not familiar with Barnard actions though, so its possible they just have funky firing pins.

I think it's just an optical shadow issue making the firing pin hole look odd. I'm sure its a nice rounded tip.

Good spotting the ejector swipe as I did notice 2 cases with a bright shiny new mark on them when I picked them up. A few weeks later they have faded somewhat.

Marty the flat primer with the ejector mark was from one of the 75gr hp loads. The case to the left and the 3 on the top right row are the 108gr eldm.
Z
P's will go and reweigh the HP bullets. They are 1970's left overs from my Dad. I assumed they were 75gr speer HP in with some hornady 75gr HP.
https://www.speer-ammo.com/products/...t-bullets/1205

Some primers harder than others. I don't recommend them as a reliable indicator of pressure.
I am an advocate of ladder testing over a chronograph.

I don't worry too much about flat primers. Too many variables. I look for ejector stamping, extraction stiffness and watch velocities. If my velocities are extraordinary compared to the manufacturers manuals I start thinking that something strange is going (although +100 fps over doesn't worry me if everything else is in order)

I have never measured case expansion because maths baffles me.

Thanks Guy's
Much appreciated the input.
Will give my Crono a work out next time out.
Z

Excessive headspace from full length sizing can also cause flat primers with mild loads.
The primer backs out of the case to the bolt face then is rammed back in as the case streatchs back to the bolt.

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Have a read of this article by John Barsness, a well respected American gun writer.

https://www.24hourcampfire.com/ubbth...mer-flattening

Hey @10-Ring right thread
Good article that
Shame he doesn’t go into what those two mistakes of his were.