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Markings on case head

NJViper91

I am getting some marks on the case head of both factory and reloaded ammunition.

AR-15 6mm Arc - 22" barrel gas+1 using a JP enterprises BCG.
Barrel was head spaced to that bolt.

I don't think the primers are showing signs of overpressure.

The gun ejects the casing between 3 and 4 o'clock.

I have a SA adjustable gas block that is in Bleed off mode.

I went back and looked at some older cases I fired and i'm also seeing the marks there too so I dont think its a new issue, just one that I didn't really notice until now.

Maybe this is normal, not sure. I was thinking of maybe getting a new bolt but wanted some input first of what could possibly cause this.

Pic with 1 casing is factory match ammo and the pic with 2 casings are the reloads.

I also included pics of the bolt and chamber.

IMG_8751.jpg
IMG_8741.jpg

IMG_8743.jpg

IMG_8737.jpgIMG_8740.jpg
 
Last edited:
Primers rounded on edges = normal
Ejector shiny spot on case head = normal on soft brass or over gassed
raised ring around primer dent = normal with over sized FP hole in bolt face

Shoot it.

Frank
 
fkimble@charter.net said:
Primers rounded on edges = normal
Ejector shiny spot on case head = normal on soft brass or over gassed
raised ring around primer dent = normal with over sized FP hole in bolt face

Shoot it.

Frank
Click to expand...
ok, good. I think the gas is good as it is deflection around 3-4 o'clock.
I am not hating the results either.

Ballistic-X-Export-2023-01-06 13:17:07.626693.jpg
 
I only have 5.56 AR bolts, so I just am not familiar with the bolt you use. Might be the pic, but your ejector looks small in the ejector hole in the bolt face.

I mention this because in your pic with the single piece of brass (factory match ammo), it looks more like an impression in the case head from a raised portion of the ejector opening in the bolt face. If you remove your ejector, is the edge of the opening smooth on the bolt face, or does it have a slightly raised burr on the edge?

The pic of the 2 reload brass case heads clearly show excess pressure signs. While others have dismissed this as soft Hornady brass, I think that generalization is overused and is misapplied in this case. While your primers appear to still have rounded corners, the firing pin impression is crated on your loads, but not on the factory loads. Primers are not a fool proof indication of excess pressure. Primer appearance is only one of many signs of excess pressure you need to be looking for.

If you read through the pictures and explanation on reading case head pressure signs on the following site, it is some good info:

Primal Rights

Primal Rights
www.primalrights.com

Don't just look at the pics, read the description that fully analyzes each load.
 
"While your primers appear to still have rounded corners, the firing pin impression is crated on your loads, but not on the factory loads."

The crater around the firing pin dent is not caused by over pressure loads. It is caused by excessive clearance around the firing pin where it protrudes thru the bolt head. If high pressure the primer flattens out. And different primers are different thicknesses and strengths which does make it difficult to "read" them.

Frank
 
Dusty Stevens said:
Thats too big of a case for an AR15. Look at that ring around that bolt face. Not much holding those lugs together.
Click to expand...
You're smarter than that! Just do the math....the pressures were reduced for the ppc/grendel/arc casehead, NOT based on anything to do with meat around the lugs but by bolt thrust. Nothing more, nothing less. Just do the math Dusty.
 
NJViper91 said:
29g leverevolutuon. 108 ELD
Click to expand...
Not sure of that load, but there is a lot of data out there on ARC and some is for bolt guns and some for gas guns ... I would verify your using correct Data.
Regardless, published data is what it is, if your seeing those type of pressure signs I would definitely back it down some.
Best of luck and be safe
 
Pres100 said:
Not sure of that load, but there is a lot of data out there on ARC and some is for bolt guns and some for gas guns ... I would verify your using correct Data.
Regardless, published data is what it is, if your seeing those type of pressure signs I would definitely back it down some.
Best of luck and be safe
Click to expand...
This was the reference I was using

6A75F63D-BDBF-419F-B950-0FF490830E83.png
 
NJViper91 said:
I am getting higher than advertised for 29 grains. I have it written down but it’s around 2615. The last test I did was bothering lever evolution and cfe223.
Click to expand...
Yeah, I'd back it down a bit. I don't have a current Hornady manual, but does it state if the test firearm was a gas gun or bolt action?
 
Pres100 said:
Yeah, I'd back it down a bit. I don't have a current Hornady manual, but does it state if the test firearm was a gas gun or bolt action?
Click to expand...
It’s a gas gun with an 18” barrel. My rifle is a gas gun with a 22” barrel so I figured that it checks out with the extra velocity.

361BEBE3-3483-4912-BECA-1516AE456CA8.png
 
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