Reading Primers....

ARH77

ARH77

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On the weekend I fired some test loads. I started at 42.0 and went up to 45.3 in 0.3 grain increments. I was using Federal 210M primers.

As the load went up the flat section on the primers gradually got bigger and bigger. But none of them were mushroomed.

There was no blot stamping on the brass on any of the loads.

None of the primers were "mushroomed" all of the primer diameters were the same when they were removed (I measured with a calliper)

It makes sense as the load/pressure goes up the flat section would gradually get bigger.

I read and hear that "flat" primers are a sign of pressure, and this is obviously true.

But at what point of "flatness" do you need to start backing off?

Is a flatter primer with no "mushroom" on it still a safe load?

Looking for some input, Thanks.

These were the extreme on each end, one on the left was 42.0 and one on the right was 45.3, both measured the same diameter and there was no mushroom on the 45.3 just a bigger flat area. All the other primers had a flat area between these two.

 
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Those look good to me.


Flattened primers are not the greatest indicator of pressure. Federal, for example, tend to flatten easier than say, CCI. So reading primers can be sketchy at best. It's just one of many things to look out for.


When you remove the brass and there is no primer, that is an indicator that you have gone too high. ;)
 
Look fine to me too! Still have a rounded shoulder so they haven't expanded to fill the primer pocket totally. Also ...... don't see any mushrooming up around the firing pin strike either. They seems to still be fully seated in the pocket, not starting to blow out or anything ....... I would say your OK from what little you can tell from primers. PS ........ depends a little bit on what brand/hardness primer you are using also as they do vary!
 
As you work up a load from the suggested starting load you will see the primers have backed out of the primer pocket with the starting load. As the load is increased you will reach a point where the primers are now flush with the base of the case. At this point the chamber pressure is high enough to cause the brass to stretch and meet the bolt face. From this point as the load is increased you you watch your primers and you can also measure the base of the case just above the extractor groove for base expansion.

Below a work up load and reading primers for pressure, with the primer on the right saying too much pressure.

pressuresigns_zps50637610.jpg


Below is an animated image of a cartridge being fired, first the pressure forces the primer out of the primer pocket. Then as the pressure increases it becomes high enough to make the brass stretch to meet the bolt face and the primers will be flush with the base of the case. "BUT" if you over resize your cases the head clearance or "air space" between the rear of the case and the bolt face increases. Meaning excess head clearance can make your primers mushroom just because they backed so far out before being reseated by chamber pressure.

HeadClearance_zpsf30a3af1.gif


Reading primers is a ball park indication of pressure "BUT" each type and make primer will read differently. A better method is to measure base diameter and see if the brass is starting to flow at the unsupported base of the case.

Below is a exaggerated example of what I mean.

flow_zps2b838d87.gif


At AccurateShooter.com many of these competitive shooters keep increasing the load until brass starts to flow into the ejector in the bolt face. When this indicator starts to show it means you have reached the elastic limits of the brass and you are "OVER PRESSURE" and need to back off one to two grains of powder. It also means you have gone over the maximum pressure for "YOUR" rifle and cartridge case, it will vary depending who made the brass and how hard the base of the case is. As a thumb rule military and Lapua brass will be the hardest and Remington and Federal being the softest.

ejectorpressuremark_zps95edb3b2.jpg


Below another work up load from right to left with the case on the far left with a stretched primer pocket and a lost primer. All the cases pictured show brass flowing into the ejector and these loads are too hot for that make of brass. Meaning time to back off the powder charge, also making a work up loads that does this and shows pressure signs will give you an idea of what is a max load in "YOUR" rifle and work below it. I do not like loading hot but as an example my Savage .223 rifle has a longer throat than any of my AR15 rifles and reaches max pressure much later than many reloading manuals do.

EjectorMark_01_zpsa4790106.jpg


Below is an example of not loading hot and being easy on your brass and rifle for my AR15s and practice ammunition. The load below is 5,000 psi below max rated pressure for the .223/5.56 cartridge.

288_zps26698a67.jpg


Bottom line, always make work up loads for your rifles until you see excessive pressure signs and then back off. I'm "NOT" telling you to load hot, and to just find your limits and what to look for. And also remember loading manuals are just ball park figures and each rifle will be different.

A man and his rifle have to know their limitations and to load safely.
 
I once had a guy at the range tell me my loads where WAY too hot and that I was going to kill myself. I had to stop immediately, bring my loads home, and disassemble them. He made this comment after looking at some brass on my bench. Round in question was 300WM out of a Rem 700. The cases he made the comments on where factory loaded Federal cases I had just fired; not handloads at all (I did have some handloads on the bench but they where in a plastic box).

Different primers will flatten at different pressures. It tells you nothing about if the round is over pressure or not because different rounds have different max pressures. If someone totally flattened a CCI primer in a 45-70 that is insane as you are probably talking 70k psi. If a Federal primer wasn't flattened in a 270 I'd say the round is quite a bit under max pressure.

If you know roughly at what pressure different primers flatten and you know the max pressure of the cartridge you are shooting you can draw some conclusion but nothing concrete. As *MALICE* said above it's just one indicator but not the end all and be all of pressure indication.

As for primers mushrooming do you mean when it craters and you get a raised ridge around the primer strike? If so that isn't necessarily a sign of high pressure as it can also be a sign of very low pressure. That happens to me quite commonly with worn out surplus rifles and light cast bullet loads. The hole the firing pin comes through is too large and the primer cup can flow around it into the bolt face. I picked up a Martini-Enfield (303 British) recently that does it on every shot with mild loads that are probably around or below 40k psi (max for 303B is 49k psi). I've even had it happen with CCI primers and loads that are listed as under 30k psi in other surplus rifles.
 
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