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

http://home.comcast.net/~kdiver/MOD_3301.jpg

[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]

....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

[kdiver58]

I just want everyone to know the picture is of factory cor-bon loads, not my reloads.
Cor-Bon 150 gr JSP 1900 fps 1200/energy. Looking at my Serria manual that is a little hotter than I thought it was.
I'm learning here .. my question is .. If it was a headspace problem whouldn't I be having it on my reloads also ?
I'm going to install the adjustable gas tube and see if that helps. Thanks for all of the help .. Keep it coming .. :grin:

[kdiver58]

http://home.comcast.net/~kdiver/MOD_3303.jpg

http://home.comcast.net/~kdiver/MOD_3304.jpg

Grew .003

[kurtz]

Grew .003

compare the two just on the other side of the extractor groove....the very bottom of the case wall....if it also grew .003 there......Danger Will Robinson.....something is bad wrong......

kurtz

[JFettig]

Does anyone know who manufactures their brass? Its possible that it has a softer head than normal(think FC .223 Rem VS FC 5.56 cases).
If its a factory Corbon load, contact them for sure.
What is the mfg of the barrel and reamer?
Jon

[kdiver58]

It's a Model 1 sales upper. I got to thinking and decided to make a CERROSAFE casting of my chamber. It looks good. The only 2 dimensions that are a little different than the Sierra manual are ... It looks like I could run my cases longer than the 1.360 the Sierra manual and my rifling lands are .085 +/- closer than they should be.
I installed a AmForte gas tube yesterday and plan on spending a day at the range Sunday.
The Cor-Bon brass is all over the place length wise. I'm getting as long as 1.365 and as short as 1.342.
The Cor-Bon brass mic's .372 before I have fired it and .375 after I have fired it.
The federal .223 GMM in my DPMS mic about the same.

[JFettig]

For some reason I think .374/5 is ok and thats what it runs after I shoot it once, I just measured an unfired case and it came to your dim.

Your M1S upper has a short throat. take a sharpie to your bullet, chamber it and see if its in the rifling. You could try seating a bullet a little long to check it too.

Jon

[Pitt300]

I think ALL throats are a little shorter by design so as not to infringe on SSK's patented .300 Whisper.
That's why they are called .300-221s or 300 Fireball.
If you want the EXACT SAME chamber you need to get SSK's or get one of the others & THEN lengthen the throat a little.
I understand that M1S & others cannot do this due to patent/trademark infringement issues.
If it's not SSK's then just seat the bullet a little deeper & get on w/life.
That's what I did w/my 300 Fireball from M1S & life is good.
My .02 worth.

[Garrett]

Interesting. I still have a box or two of CorBon subsonic .300 Whisper ammo from 3 or 4 years ago. It all used reformed 5.56 mil. brass.

[kdiver58]

Well I shot with the gas tube shut off and it still spit primers. All were super sonic cor-bon 150gr JSP listed at 1900 fps.
I opened up the tube 1.5 turns and the gun cycled fine unless it dropped a primer.. I even have video of me having a fit when it jammed my gun with primers. The stuff was VERY accurate ... 1.7 inch 10 shot group at 100 yards.

[kdiver58]

http://home.comcast.net/~kdiver/primersWEB.wmv

[JFettig]

If it is factory ammo, send it back! Its definitely not acceptable but thats the only thing you can do.

Jon