Pressure signs - pictures

[taliv]

i don't often push the limits of pressure when reloading, so i figured people might be interested in seeing a pretty good example of some common pressure signs: "flattened primers" and "primers backing out"

the fourth case is exactly how i picked it up off the ground after it ejected from an AR15.

 

[Shoney]

Pressure sign for rifle brass are good guide posts. But you must remember, there are no reliable pressure signs for most straight wall pistol cartridges.

 

[mrkubota]

Looks more like a headspacing issue to me....or maybe short stoking if this is a short barreled AR. you can see the black soot that leaked out around the protruding primer. Probably the reason it didn't reset back into the pocket like the others.

With a high pressue load you'll usually see the primer flow out flatter into the primer pocket mouth chamfer too.

 

[taliv]

the others are not loose, and i guarantee there are no head-space issues with that chamber/bolt. the bolt and barrel were purchased together from white oak as a headspaced pair, and i checked it myself with the gages. it is a 16" barrel.

 

[steve4102]

What's the load? A backed out primer is usually a sign of Low pressure and not high pressure.

 

[Jim Watson]

They don't look flattened to me. The edges are still fully radiused. The indents look strange, though. How old is the brass? Maybe the one with the backed out primer is just worn out and loose.

 

[scrat]

i agree its more of a bad batch of brass. the one with the loose primer probably has a worn out primer pocket.

 

[snuffy]

What's the load? A backed out primer is usually a sign of Low pressure and not high pressure.

Bingo! Classic sign of LOW pressure and a case that's had the shoulder set back too far. That creates an excessive headspace, regardless if the headspace checks out okay.

The firing pin shoves the shell forward up against the chambers shoulder. It fires the primer. Then the pressure inside the case causes the case to grip the chamber walls, but the pressure does not get high enough to stretch the brass back against the boltface. The primer can still move, it's unsuported, so it backs out of the case. If the pressure was higher, it would stretch the case, at the web area, then the primer would be reseated.

 

[jr81452]

i'd say high pressure was a factor. look at the second in from the right, the pin strike mark is poped out. and the one on the right the pin strike looks like it started to pop out, but the primer backed out before it got out to far.

 

[mc223]

Other than the case at third from left, they look like low pressure to me also. The primer of that other one looks as though the primer was beginning to flow. Or another thing I noticed is that the firing pin dents seem deep as illustrated by the straight area above the radius. This could account for the third from left as the primer material is being streched too far and thinned, then flowing back towards the bolt. If suffeciently thinned this could lead to pierced primers and firing pin damage.
There was no mention of what primer or loading was being used. I would suspect WSR or CCI primers and 748 or 4895.

 

[DaveInFloweryBranchGA]

No flow of the primers causing squared primer corners. No cratering of the primers, though the pic is making the firing pin punch holes look odd. They are certainly deep with a definate thread of pierced primers. A backed out primer. I'll side with the guys that think the cartridge shoulder is bumped back too far and isn't coming forward fast enough in time to prevent the primers backing out. I'll also vote low pressure. Need a little bit more "bang" and less "whoosh" for that short barrel and quick cycle time. Wouldn't hurt to investigate the buffer and buffer spring timing over at AR15.com or another of those AR forums.

Regards,

Dave

 

[USSR]

They don't look flattened to me. The edges are still fully radiused. The indents look strange, though. How old is the brass? Maybe the one with the backed out primer is just worn out and loose.

+1. No signs of high pressure with those cases.

Don

 

[Picknlittle]

Okay,..now I'm puzzled. These pics show exactly what I found when building loads for my 35 Whelen. As loads approached max, some primers were backing out but were not flattened. As I understand flattened primers, I should be able to feel somewhat of a knife edge around the primer base with my fingernail. Mine were all still rounded. The load I finally selected of 63gr BL-C(2) with 200 gr hornady sp did not show signs of backing out during testing, but a few did back out at the range a few days ago.
Same rounded primer edges.

BTW, this is all new remington brass.

 

[taliv]

i'm very intrigued by some of the responses and theories. thanks for the feedback. i'll provide you some more information here, and more of my own opinion.

the load is the same bullet as mentioned here, at a similar velocity. http://btammolabs.com/tests/4.htm and there is no published load data, so I won't discuss the details, but when i spoke to the mfg, they were surprised and indicated it was very, very hot. Based on the chrony results, and the amount/type of powder, I'm fairly certain these are at the upper end of the normal range and not the lower end.

the brass was 2x fired RP (now 3x fired) from a lot of 10,000 pieces, of which i have fired a couple thousand a 3rd time with no issues. I'll post pictures later today of other spent brass from the same group (i.e. fired same number of times) so you can see how much deeper the normal primer indents from this rifle are, and how much more rounded the other primers are.

it's not the pic that's making the indents look that way. they look odd in person and not very deep, but much shallower than normal.

also, it's not a quick cycle time. it's a mid-length gas system with 16" barrel.

my personal theory is that the the pressure made the primer very loose in the pocket (it takes almost no force to move in and out, like, you can blow on it to move it) and when it was ejected, the centrifugal force of spinning or when it struck the ground caused it to slide halfway out.

snuffy's low-pressure theory is interesting, but i've also put probably 300-400 subsonic and nearly subsonic rounds using the same lot of brass through this same gun, and that hasn't caused any primers to back out.

but to your point about the shoulder being set back too far, i DID run these cases through my sizer die twice during this load process. once to size them so they would fit in my case trimmer and again after they were trimmed just because i'm loading on a progressive and it's easier to let them feed through the case feeder than to stick them in station 3 by hand. however, between and after the sizings i verified it was set correctly using a case guage.

 

[Doug b]

Any high pressure loads I've experianced look the opposite of this.

 

[taliv]

kind of a crappy picture cause i had to take it indoors using my surefire as a light source i'll try to get a lower angle view later today

case on the left is a normal firing pin strike (55g fmj over 24g 2230c). case on the right is one of the previous 4 above. see how the normal indent from the firing pin is twice as deep and round. indent on the right is flat with a small raised portion in the center.

 

[Walkalong]

Gotta be a bad piece of brass. If there was enough pressure to expand the primer pocket enough that the primer was loose it would have showed on the primers, trust me on this one. Anyone who has blown a primer can tell you that.

 

[Mal H]

I've never seen a firing pin indentation like that without the primer also loosing all or most of its radius and flowing to the edge of the pocket. I wonder if it can be caused by loose pockets (as surmised by several) with the firing pin pushing the primer back into the pocket with just enough power to still fire the primer. That would allow for a lighter than normal indentation.

If you haven't yet measured the case diameter at the web, please do so with a good micrometer and see if there is any appreciable difference from a "normal" case of the same manufacture and fired from the same rifle.

 

[taliv]

0.3291" for the one with the backed out primer
0.3289" for the "normal" one in the last picture
0.3290" for another one of the 4 in the first post

 

[The Bushmaster]

taliv...Your photos do not indicate over pressure. They indicate a head space problem or you have set the shoulder back too far. FLATTENED primers do not indicate over pressure...Besides I didn't see any flattened primers in your photos...

Check your head space and insure you didn't set the case shoulder back too far when you resized them...

The one with the backed out primer indicates that the round fired and did not slam against the bolt face allowing the primer to back out. Most flattened primers start out like that then are slamed against the bolt face thus reseating the primer and causing it to flatten. The less head space the less flattened the primers will be...In most cases...

 

[Mal H]

0.32xx

Are you sure? The nominal diameter at the web is 0.3773. Yours shouldn't be smaller by as much as 5/100ths.

I measured several R-P .223 Rem cases I have (fired approx. 2X). They were all 0.3733.

Ignoring the second significant digit (mic problem?), it does look like there is some minimal expansion at the web, but only about .0001" to .0002". That could be attributed to differences in cases and not necessarily pressure. I don't get concerned until there is a .0005" increase or more.

 

[USSR]

I've never seen a firing pin indentation like that without the primer also loosing all or most of its radius and flowing to the edge of the pocket. I wonder if it can be caused by loose pockets (as surmised by several) with the firing pin pushing the primer back into the pocket with just enough power to still fire the primer. That would allow for a lighter than normal indentation.

+1. There are several possibilities here, but high pressure is not one of them.

Don

 

[taliv]

oh, sorry, Mal. i thought you wanted me to measure the diameter over the primer in extractor groove.

over the web
0.3755" (backed out primer) (edit... i copied it wrong first time, and these are max diameters as cases are slightly out of round)
0.3750" (normal)
0.3755" (3rd case in the group of four in first pic)

 

[Mal H]

Ok, that is a sign of excessive pressure. The primers honestly don't look like that is the cause, but the web expansion is a much better indicator.

As Steve asked above, what's the load? You gave the load for the normal rounds, but left it out for the questionable ones.

 

[taliv]

bushamster, as i mentioned previously, i have a couple thousand rounds of normal loads that have all been prepped and processed the same way and I checked the cartridges to make sure they were sized properly with a case gauge. also, the barrel/bolt combo was headspaced by whiteoak. these rounds were numbers 1953-1957. (there were 5 but i lost one, as they were getting flung quite a ways).

the point is that if there were a headspace problem or if the cases were sized incorrectly, it would show up on all of them, because all these cases were run through the same press at the same time and dumped in a big bucket that i grabbed 5 cases from.


edit: mal, that's a good idea. i never thought to measure the case diameter. i assumed they would all be the same (the ID of the chamber) and not vary by pressure.

also, i mentioned the load in 2nd paragraph of post 14.