Soft Cor-Bon brass ?

[kdiver58]

I went to the range yesterday to work on a good sub-sonic load that would cycle my AR.
While I was at it I shot a few of the 150 gr 1900fpc rounds I bought from cor-bon. Look how the brass was deformed and it even spit a couple of primers. I found that odd.
I settled on 11.4 gr 1680 over a 220 gr SMK.. It fed like a champ from my Magpul 20 round mag.
Below is a pic of a unfired cor-bon, a fired cor-bon and one of the cases with the missing primer. Look how the heads deformed on last picture..

K

[kurtz]

Are you using a pistol or carbine length gas system?.....

[Ron458]

I second that "Are you using a pistol or carbine length gas system?....."
Looks like they are too hot for your setup!

[kdiver58]

Carbine length gas system. It's a stock DPMS lower. I tried them with both of my lowers one is a factory A2 style lower and the other is one I put together with an adjustable stock. I don't have any flattened primers or any other pressure indications. I'll get a gauge pin set and measure the primer pockets and compare them to my .223 pockets.
1900 fps is not all that hot. I did get an adjustable gas tube today .. I'll try that ..

[kurtz]

head space maybe.....I drive my whisper and 7.62x40 loads hard...thats a pretty healthy ejector strike in the base....

kurtz

[JFettig]

Originally Posted by kurtz

....thats a pretty healthy ejector strike in the base....

kurtz

I agree, it looks like either those heads are very soft or your loads are very hot. You shouldn't see the circle from your ejector and line from the extractor. Your brass is flowing back into those spots on your bolt.
I was experimenting with my .223 and had the same thing when I dropped 27.5gr of H335 to reach 3150fps out of my 16". I backed it down a bit.

Measure the diameter just above the extractor groove on the case and compare it to another unfired case, it shouldn't be more than .001" larger.

Jon