Soft Cor-Bon brass ?

[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