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Posted: 10/22/2014 3:43:04 PM EDT
[#1]
Flattened cratered primers are telling you that you are flirting with disaster. I put a lot of stock in these warning signs.
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Posted: 10/22/2014 4:00:34 PM EDT
[#2]
Quote HistoryQuoted:
Flattened cratered primers are telling you that you are flirting with disaster. I put a lot of stock in these warning signs. Yea, I am probably at or beyond where the Dragons be. 
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Posted: 10/22/2014 4:08:19 PM EDT
[#3]
I don't put much stock into simply flattened primers, especially when I'm running CCI 400's which have a thinner cup and flatten a lot easier.
I'm getting primer cups "flowing" to an extent into the primer pockets I've reamed on LC brass where it creates a slight mushroom cap. I'm about 3% below max load per Lyman #49 on my 223 loads. Chrono's are great for this - flattening velocity with increasing powder is a solid sign you're in the danger zone. |
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Posted: 10/22/2014 4:10:17 PM EDT
[#4]
Somewhere in Speer No. 13 is a paragraph stating that you could be 30% over pressure and still have normal looking primers. They had a picture showing that. So, yeah, if the primer is flattened, you're in dangerous territory.
Other signs to watch for--sticky extraction (hard to notice this in a semi auto) and brass deformation (hard to see in fully supported chambers.) |
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Posted: 10/22/2014 4:37:26 PM EDT
[#5]
I am heavily invested in reading primers for signs of pressure because I have no alternative methods available to me.
For rifle rounds, I am careful in sizing to ensure I don't have excessive headspace which can lead to false signs of high pressure. For pistol rounds, I ensure headspace is reasonably small for the cases used during load development (case length) and ensure the bullet is not seated on the lands. With these precautions, I get decent correlation with pressure data (max loads) in my manuals. |
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Posted: 10/22/2014 4:56:53 PM EDT
[#6]
And I thought I would be a lone voice here....
I put a lot of stock into primer appearance as primers are usually the weak link in the whole chain. The primer cup is the first thing that fails. I look at it as part of a whole, though. If the rifle/pistol has one of those prewar (one) huge firing pin holes, the primer will likely fail at relatively low pressure and a bit of load work or smithing work is in order. If I am loading something non-standard, a firing pin wipe could be a sign of early unlocking and I need further diagnostic work. The list can go on. |
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Posted: 10/22/2014 5:06:31 PM EDT
[#7]
It would depend a lot on what specific primer you're using, and how it behaves in known-pressure loads. Some primers are thinner than others, some are harder, some are just plain flimsy. If you have a track record, say with CCI primers, and their #500s look a certain way with "hot" loads, you have something to compare to. Unless you have that sort of benchmark, you're just looking at a bit of brass that may or may not tell you anything.
Given experience with a specific primer, I would put a LOT of stock in connecting a really flattened primer with an extra-sharp recoil and really loud report to "maybe this load is over the line." THEN, I'd take a look at the fired cases, see how the primers looked when punched out, and how the primer pocket looked too. But a load that makes really flat primers would be a big red flag for me. |
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Posted: 10/22/2014 5:21:40 PM EDT
[#8]
I always look at the primer, but it dosent always tell you everything.
here is an example. using CCI 450's in my mk262 duplicate and RL15 the primer looks like it just came from a plinking load except that im over max charge per all the manuals. |
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Posted: 10/22/2014 5:38:18 PM EDT
[#9]
Using a Micrometer to measure brass expansion is also a valid method. I would pay the primers close attention.
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Posted: 10/22/2014 5:49:22 PM EDT
[#10]
I look at the primers. Always have. If I'm working up a load the primers won't be flattened at the bottom and will start to flatten out as the pressure builds.
Does one brand show flattening at lower pressures than others? Maybe so. I've measured primer cup thickness on a couple different brands and there is a difference in thickness, sometimes as much as 25%. I also know my CZ's will light off Tula small rifle primers (supposed to be thicker/harder than small pistol primers) without problems. Something to try if your brand is flattening out primers at lower pressures/velocities. |
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Posted: 10/22/2014 6:09:15 PM EDT
[#11]
Quote HistoryQuoted:
It would depend a lot on what specific primer you're using, and how it behaves in known-pressure loads. And the firearm in question. I have one rifle where, because of the rather generous firing pin hole, ALL loads "crater". ALL OF THEM. Any indication as to pressure that I get from the primers, when shot in that rifle, will have to come from the outside radius of the primer. |
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Posted: 10/22/2014 6:21:44 PM EDT
[#12]
Yes I look at primers but I've been looking at them for about 28 years or so. To get accurate reads you need something to compare to. Nothing beats or can replace experience for some things and primer reading is one of those things.
Primer brand and part number and what firearm they are being used in are just a couple things that can change what a fired primer looks like. What is this cratered thing? Its been my experience that a very deep firing pin crater is usually from a very light load. When they come out flush with the back of the case head and no gap between the primer and the brass I'd say too hot but I've seen plenty of once fired factory brass look exactly like that. Go figure. 
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Posted: 10/22/2014 6:47:46 PM EDT
[#13]
Quote HistoryQuoted:
I've measured primer cup thickness on a couple different brands and there is a difference in thickness, sometimes as much as 25%. The bigger unknown is the brass hardness in the primer cup. Notice how hard brass case heads are. Especially in higher pressure rounds. Work hardened brass has far more strength than annealed brass. |
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Posted: 10/23/2014 9:59:32 AM EDT
[#14]
I put a lot of stock in a flattened primer be over pressure but just because it is not flattened I don't assume it isn't over pressure.
If that makes sense. Posted Via AR15.Com Mobile Here is a photo from a test I did a while back. For reference Hornady 168gr Match ammo is 52k psi tested with the same system. You can see in this case the pressure is very high and flattening is slight. 
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Posted: 10/23/2014 11:25:40 AM EDT
[#15]
I don't put a ton of stock in the primers. I make sure I stay within the listed loads and rarely run max loads. Very few chambers on the market cut to SAAMI specs are going to have problems with even heavy published loads. I also use a chronograph periodically which helps for a sanity check compared to the published loads.
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Posted: 10/23/2014 11:33:34 AM EDT
[#16]
Better safe than sorry. KABOOM
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Posted: 10/23/2014 5:38:59 PM EDT
[#17]
Quote HistoryQuoted:
I put a lot of stock in a flattened primer be over pressure but just because it is not flattened I don't assume it isn't over pressure. If that makes sense. Posted Via AR15.Com Mobile Here is a photo from a test I did a while back. For reference Hornady 168gr Match ammo is 52k psi tested with the same system. You can see in this case the pressure is very high and flattening is slight. http://i3.photobucket.com/albums/y59/glock2027/CIMG1902_zps77148424.jpg |
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Posted: 10/23/2014 5:55:00 PM EDT
[#18]
edit to delete .... OP , I have no business talking pistol reloading and incorrectly posted rifle opinion before reading from the start... sorry
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Posted: 10/23/2014 6:29:03 PM EDT
[#19]
Quoted:
10mm, Blue Dot, 180gr XTP. The primers are just starting to flatten at 11 gr. Hornady lists 10.7 gr as max. All that crap about flat primers is not statistically valid or reliable especially with gas operated systems like the AR. As for Case Head Expansion (CHE), by the time you see it you are over pressure. |
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Posted: 10/23/2014 6:51:11 PM EDT
[#20]
Quote HistoryQuoted:
Where do you measure the head? At the front of the extractor groove? Quote HistoryQuoted:
Quoted:
I put a lot of stock in a flattened primer be over pressure but just because it is not flattened I don't assume it isn't over pressure. If that makes sense. Posted Via AR15.Com Mobile Here is a photo from a test I did a while back. For reference Hornady 168gr Match ammo is 52k psi tested with the same system. You can see in this case the pressure is very high and flattening is slight. http://i3.photobucket.com/albums/y59/glock2027/CIMG1902_zps77148424.jpg Well I am measuring with a micrometer so that covers a 1/4" area; so from where the groove angle ends to 1/4" forward. Right where the angle ends it always seems to be smaller(by a tad) where the heaviest part of the web would be. |
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Posted: 10/24/2014 4:33:21 PM EDT
[#21]
Quote HistoryQuoted:
Well I am measuring with a micrometer so that covers a 1/4" area; so from where the groove angle ends to 1/4" forward. Right where the angle ends it always seems to be smaller(by a tad) where the heaviest part of the web would be. Quote HistoryQuoted:
Quoted:
Quoted:
I put a lot of stock in a flattened primer be over pressure but just because it is not flattened I don't assume it isn't over pressure. If that makes sense. Posted Via AR15.Com Mobile Here is a photo from a test I did a while back. For reference Hornady 168gr Match ammo is 52k psi tested with the same system. You can see in this case the pressure is very high and flattening is slight. http://i3.photobucket.com/albums/y59/glock2027/CIMG1902_zps77148424.jpg Well I am measuring with a micrometer so that covers a 1/4" area; so from where the groove angle ends to 1/4" forward. Right where the angle ends it always seems to be smaller(by a tad) where the heaviest part of the web would be. |
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Posted: 10/25/2014 11:32:39 AM EDT
[#22]
I look more at extractor marks especially as I run the softer primers.
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