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4/15/2016 9:00:56 PM EDT
I have a 9mm carbine and I have had all kinds of trouble with it.

The lower is a Rock River with a Rock River 9mm kit on it. This lower formerly had a Colt upper on it. It ran wonderfully for many years. I decided to SBR that Colt upper and put it on a Quarter Circle dedicated lower. Works great.

But, that left me with a lower and kit.....So Palmetto had a special on uppers. I bought the 16" upper and bolt. It would lock up on the first hammer fall. Piece of shit. Sent the bolt off and had it ramped by M60 Joe.....took out the Rock River hammer and put in a rounded DPMS style hammer, put in KNS pins----all the shit you're supposed to do. Gun will not reliably cycle. It stovepipes and crushes cases. Does this several times out of a magazine. Ammo makes no difference, magazines make no difference- CP Prod, ASC, Palmetto, Brownells, Metalform...tried them all........ Ah, ejector you say.....Nope. Bent it until it rides tight up against the bolt. In fact, probably too much as I think it's dragging and slowing the bolt.....Will bend it back a little to see if that helps.

I am about at my wits end with this gun. I need to get it up and running reliably. Any help much appreciated.
4/16/2016 11:59:25 AM EDT
[#1]

Greetings,

  Weight of buffer and/or strength/length of spring? Just a thought. Best of luck!

Regards, Jim
4/16/2016 3:38:26 PM EDT
[#2]
I can't really say...it's whatever comes with the Rock River kit....which has run good with the old Colt upper and I assume would be correct......
4/16/2016 3:45:35 PM EDT
[#3]
how does it run on the sbr lower?

while you can't go the other way, why not give the longer upper a try on the sbr to make sure the issues follow the upper.

also swap bolts and see if perhaps it is the grab that is the issue vs actually ejecting.
4/16/2016 8:23:24 PM EDT
[#4]
I'll see if I can get to the range tomorrow and swap some things around....just very frustrating....
4/16/2016 8:35:15 PM EDT
[#5]
yep, I get that.
helps to have a functioning setup you can swap parts around on till the failure moves.
should be fairly easy to narrow down.
4/16/2016 9:53:05 PM EDT
[#6]
Can you post a picture of the ejector hook from the side? I'm betting it has a downward angle on it.....try slowly pulling the bolt back with a round chambered and as it hits the ejector see where the round is going........I'm guessing you'll see it move toward the bottom of the ejection port.....if so...take a dremel with a cutoff wheel or a file and square up the ejector......that should solve the issue.
Rudy
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