reading pressure by the primer in a semi

[1sailor]

I was always told that examining your primers will give you an early indication of excess pressure. Lately though I've read a couple of posts in different places that say that those pressure signs are only relevent in a revolver and that they won't always show up with an autoloader. Because of the local shortage of small pistol primers I had tested a few loads using SP magnum primers in my 9mm. Examining the primers afterwards and comparing them to standard primers fired with the same loads I don't see any difference. These are no where near being maximum loads. They're kind of middle of the road loads using berry's plated bullets loaded to a little below maximum lead bullet loads. Anyone have the straight scoop on semi auto primers showing warning signs of pressure.

[jepp2]

While primer flattening is probably the most talked about indication of pressure, in my experience it is not very reliable. It is a better indication of headspace.

Semiauto pistols tend to be more challenging to determine increasing pressure since many of the normal methods don't work. At the end of my post I will list a link to the best listing of the many ways to check for pressure. But, many will not apply for your instance. So for autoloading pistols I feel the most accurate are ejection and appearance of the outside of the fired case. But I know my pistols and know what normal looks like.

The best and most accurate indication of maxium loads is a properly used chronograph. But I'm guessing you don't have access to one.

For 9mm loads, due to the extreme range of OAL (1.010" to the SAAMI max of 1.169") coupled with folks that like to use fast burning powder and a cartridge that can dramatically increase in pressure with as little as 0.020" increase in bullet seating depth, you have a perfect storm.

I know that I need 24K typically to function the variety of 9mm pistols I shoot, and I load toward the maximum OAL of 1.169". So I use QuickLoad calculations for my initial loads and adjust from there.

The promised link on the many indicators of excessive pressure.

[MichiganScott]

After reading the link, it should be obvious that there is no reliable method of determining high pressure other than lab equipment.

[BlueOvalBandit]

Primer flattening in revolvers.... don't even bother reading it. Just by the nature of revolvers once fired the primer will back out some then the whole case will slam against the recoil shield and reseat the primer. The reseating often flattens primers even safe loads. Cratering is another story but can also be a function of firing pin/ pin hole or bushing fit in addition to pressure. Like said a chrono is your best friend when evaluating loads in pistols.

[Nevada Ed]

If you reload you must know that a load that works in 70 degree weather might not be within specs at 90 degree weather !!
I had a 22-250 bolt freeze up on me one hot summer day at the rifle range with a nice "97%" load ..............from a plastic box of ammo sitting out and getting warm. This primer looked very "Safe" at 70 degrees.


Same goes with loads with new powders or new primers that have not been tested before............

Sometimes, safe is a term that we have to look at a little closer................and think, "Is this safe".

Good shooting.

[1sailor]

I agree with everyone here regarding safe loads. However I am not trying to see how far I can push it. Only trying to determine if my load is still safe with SP magnum primers. Published data shows me a starting load of 3.8gr of Universal (for a lead bullet) and a max load of 4.6gr (midrange load for a jacketed bullet). I am loading 4.2gr of universal with a Berry's plated which recommends the maximum load as being midrange for a jacketed bullet. I tried mixing a magazine of my magnum primer loads with standard primer loads and could detect no difference in sound from round to round. The empty cases also seemed to land in the same location as with standard primers. I have fired thousands of rounds using the 4.2gr load with standard primers. I'm just trying to find a safe load using magnum primers which still seem to be available even when the standard primers are impossible to find around here. I suppose I could back off a tenth on the charge if using the magnum primers. I live out in BFE and traveling outside my area to buy primers is a 250 mile roundtrip in a gas guzzeling pickup truck. I also should point out that I seat to the maximum OAL that my pistols will accomodate.

[358156hp]

Many semi-autos have sloppy chambers, coupled with supported or non-supported chambers. I just give the case a quick look before and after tumbling, cull anything objectionable, and move on. The same with primers. Once I realized one of my hand primer seaters slightly flattened the primers, and that different lots of factory ammo had flattened primers from manufacturing, I gave up on that. I do watch for loose primer pockets when reloading, and call it good from there. There's just no 100% consistency in primer seating that allows me to comfortably use primer condition to gauge anything.

[125JHP]

When I'm working up loads in a semi, I label my cases and keep them grouped together after firing. I note the feet & direction they land from my firing position. Then after visually inspecting them by naked eye and hand magnifier, I photograph them under a microscope, which shows a lot more detail.

This one has the primer strike indent flattened but yet the shoulders are still rounded. I feel this one is high pressure in the gun it was fired in as this doesn't happen in my other 9mm. Also instead of the normal 4-6' this gun throws this load 6-8' Something is happening here.



Here is a factory 147gr subsonic round that seems to show pressure signs even though it should be well within limits. Primer looks flat with some minor cratering and shearing at the firing pin smudge... is this a False Reading ????



and last this one is a 124gr HBFP with 4.8gr WST pushing just over 1000fps and tosses brass 4'~6' which is typical of factory loads. Notice how flat it is and how it fills the pocket. This one is a little more flattened than normal for this load... maybe it is the brass I used that day. I shoot this load all the time.

[shovelwrench]

The problem with the magnum primer is its made to withstand higher pressure, therefore, it'll show less sign of pressure in a standard loading.

Is your load safe with the magnum primers, probably..

[Nevada Ed]

One thing to rember when loading near or at maximum loads that have worked in the past........................
that new batches of powder,primers and bullets can be different than the last components that you used last............

Harder copper jackets,faster powder,hotter primers etc. etc.......

One reason to back off on your first loads to see "What's What" !!

[OKFC05]

I was always told that examining your primers will give you an early indication of excess pressure

For handgun cartridges like 9mm, it won't.
Here's a specific example: Some shooters at our club load "9mm major" which will destroy a typical 9mm semi-auto. They are loaded for special barrels in Open competition guns.
The brass I pick up from this is fine, and reloads normally. Ordinary ammunition shot in a jugged chamber or one with gross headspace will look awful.
Guessing at pressure by looking at primers is a good way to destroy a gun.

[johngalt]

I don't believe reading primers tells you anything about pressure in a pistol cartridge. All of my reloading manuals talks about flattened primers in 50,000+ psi rifle cartridges. They say nothing about pistol cartridges.

I shoot a lot of .45 target rounds - 185 gr LSWC + 3.9 gr Bullseye. I doubt it is even 10,000 psi, and I've seen flattened primers.

[DWalt]

As everyone has stated, fired primer appearance means nothing regarding chamber pressure. However, if I am working up loads, I always look for some change in fired primer appearance. If I see something unusual happening, such as excessive flattening or cratering, I usually stop.