AR15 Pressure signs?

Status
Not open for further replies.
x_wrench

x_wrench

Member
Joined
Oct 25, 2010
Messages
906
Location
michigan
Hi, I am a little concerned about the primers in the brass that I shoot from my AR15. I reload, and I was taught that flat primers were the first sign of hi pressure. well, EVERY case that comes out of my AR has flat primers. I have tried loading every powder to its starting load, which still resulted in flat primers, even factory ammunition have them. the only piece of brass that I have ever fired was one piece where I loaded one round with IMR Trail Boss, which obviously did not cycle the gun. I PXL_20220529_144958527.jpg PXL_20220529_134509835.jpg have come across flattened primers in my other rifles before, when loading top loads, which were easily cured by reducing the charge.. is this normal for a gas gun? this is my first semi auto rifle. so I am still learning about it.
 
I'm not an expert, but those don't look bad to me. 223 Remington/5.56 NATO is a relatively high pressure cartridge. I've picked up brass at matches that had pierced and missing primers. I'm not implying that's okay by any means, but evidently some people like it really hot.

How do they shoot accuracy wise?
 
A flat primer usually has been extruded such that the outer edges have flowed into the primer pocket and only a sharp crisp line remains between the primer and the case. The primer itself is often very very flat and machining marks in the bolt face have been impressed upon the primer.

Those are not flat primers.
 
Sometimes pressure signs are not apparent until it is very severe that can be attributed to very tight chambers and the brass being used. A quick way to check is to measure the brass before loading especially the base and immediately after firing to determine the amount of obturation of the brass to ensure it is within specs. This is really not a very scientific way of determining high pressure by any means but if a reduction in your load by 10 % makes the brass stay within specs then you may or may not have a (hot) load. As with all firearms some will take very high pressure without any discernable effect and others will exhibit problems immediately.
 
x_wrench said:
. . . I was taught that flat primers were the first sign of hi pressure.
Click to expand...
'Flat' is a common term, and is confusing in this case. Flat primers are fine; primers that have been extruded completely into the corner of the pocket and breech face are not.

To illustrate: PXL_20220529_182333846.jpg

On the left, a normal primer, from factory ammo, showing no cause for alarm. On my the right, an innovation from ole Three Finger Ned, trying to get 9mm ballistics in a .380ACP. That small pistol primer is extruded beyond the outside of the pocket.

So, when your primers match the left, you're nearing max pressure. If you see primers like on the right, make different life choices.
 
There’s a huge difference in standard primers and magnum primers. Standards will flatten easier and give you a feel for what’s going on. (I just recently learned this on THR:thumbup:)
 
Examining gas gun rounds for flat primers will not work as a pressure indication unless you fire lubricated cases. I do this in load development. An oily or greased case cannot grip the chamber walls, so the whole thing slides back as the pressure builds. The primer is then pushed into the pocket when pressures are low.

When cases are dry, and the chamber is dry, the case is fixed in place by friction, the primer backs out, and as pressures rise, the sidewalls eventually stretch, stuffing the primer back into the pocket. Primers that appear rounded with case lubrication look flat when fired with dry cases and dry chambers. Obviously the case lubrication did not lower pressures, so what is happening, is that when the primer backs out of the pocket, it expands due to rising chamber pressures. And then it gets stuffed back into the pocket when it is more or less, muffin shaped.

However, the 5.56 is a tricky round to read primers because the thing is running so hot. All that poodle round has, is velocity. And it was jacked up on pressure steroids the day it was introduced into the military inventory.

So, here is my advice. If you have leaky, blown, or pierced primers, cut the load by one half grain, and keep cutting the load by a half grain, till you stop popping or piercing primers.

If you cases look like this, you might want to cut the load by two grains to start!

HhVuFR6.jpg
 

Attachments

  • HhVuFR6.jpg
    HhVuFR6.jpg
    100.2 KB · Views: 46
Last edited:
The only one I see in the picture that I would call flat is the leftmost one in your hand, and that one is not severely flat, just getting up there on the load if they were all like that. I do not see any other pressure indicators such as cratered firing pin dimples, extractor swipes, or ejector rings, so I see no cause for concern.

See Slamfires pictures above for what cratered primers and ejector rings look like. That load is HOT!
 
Last edited:
Slamfire said:
Examining gas gun rounds for flat primers will not work as a pressure indication unless you fire lubricated cases. I do this in load development. An oily or greased case cannot grip the chamber walls, so the whole thing slides back as the pressure builds. The primer is then pushed into the pocket when pressures are low.

When cases are dry, and the chamber is dry, the case is fixed in place by friction, the primer backs out, and as pressures rise, the sidewalls eventually stretch, stuffing the primer back into the pocket. Primers that appear rounded with case lubrication look flat when fired with dry cases and dry chambers. Obviously the case lubrication did not lower pressures, so what is happening, is that when the primer backs out of the pocket, it expands due to rising chamber pressures. And then it gets stuffed back into the pocket when it is more or less, muffin shaped.

However, the 5.56 is a tricky round to read primers because the thing is running so hot. All that poodle round has, is velocity. And it was jacked up on pressure steroids the day it was introduced into the military inventory.

So, here is my advice. If you have leaky, blown, or pierced primers, cut the load by one half grain, and keep cutting the load by a half grain, till you stop popping or piercing primers.

If you cases look like this, you might want to cut the load by two grains to start!

View attachment 1081440
Click to expand...
That's hot.
 
Another reason one might have flat primers is due to head space. Upon shooting the round, the cartridge hits the bolt with such force that it flattens the primer. I also like to look at primers for punctures or cratering from the firing pin, @edwardware and @Slamfire have excellent demonstrations that show high pressure signs. Also @Slamfire shows another reason to suspect high pressure signs, and that is the headstamps. You can see indentations where the case was slammed into the bolt with higher pressures exerted from normal load data used even if the data used was at recommended max loads. Your cases as far as I can tell do not demonstrate high pressure.

If you are concerned you could reduce your load by 10%, my experience has shown me that my most accurate loads on all my rifles, including AR's have been at mid load levels never at higher loads.
 
Cutting to the chase, those primers look just fine :thumbup:
... mahvelous in fact.
:)


ps: Read & heed Slamfire, especially on the benefits of
clean/polished/slick case/chambers (lubed even)
;)

.
 
Primers look fine. I don't dip my cases or bullets in grease, but I like smooth chambers and tumble my cases with brass polish which leaves them slightly slick.
 
Thanks guys! I am surprise how many replies in a short time. Slamfire, If I saw cases like that coming from my gun, I would have 2 immediate reactions. 1st) I would be thanking God for keeping me safe during the firing of those rounds, and 2nd) I would be packing things up to take my loads home to tear them down and drop the charges down a substantial amount!
 
Status
Not open for further replies.

Similar threads

K
  • Locked
Help Reading Pressure Signs (Rifle)
2
Replies
41
Views
2K
kingmt
K
Float Pilot
  • Locked
Cooler Temp 6.8mm SPC experiments, STAG AR getting better..
Replies
2
Views
565
HorseSoldier
H
Float Pilot
  • Locked
Tried some 6.8 loads and factory loads today, not impressed yet
2
Replies
31
Views
2K
rbernie
rbernie
K
  • Locked
Primer pressure signs
2
Replies
31
Views
1K
Kwaynem
K
D
  • Locked
AR-15s and Primers
2
Replies
30
Views
2K
HankC
H
Back
Top