AR308 Help. Cam pin gouging upper receiver

arlaunch

arlaunch

Active member
It looks like the the cam pin is doing the damage on the ejection cycle but not sure?

Are your large platform AR's all clean and smooth inside like the 15's?? Or do the big ones all have what looks like damage inside?

The damage is happening to the rear part of the recess, that allows the cam pin/bolt to rotate into battery after it has stripped a round.
 
I just finished my first AR 10 which is in 243 Win. Haven't fired it yet so I don't know the answer but will be watching this thread.
 
Does the cam pin shows signs of rubbing also. I have 4 and haven't seen this. I used tool craft BCG's and Aero uppers. Something sounds definitely to tight. Mine are polished up inside like a 15
 
I haven't ever noticed that on mine but wasn't looking for it either. It just looks like the recess wasn't quite big enough for the bcg you're using. Just judging by the pics, if everything was running good I'd probably clean up that small area in the upper to remove any burrs and run it. Curious what brands of parts?
 
Just throwing out ideas but is the cam pin to bolt hole fit excessively loose and or does it rotate some when the firing pin is through it?
Secondly it appears your rifle has an ar15 rifle length gas tube in it. From what I have seen many lr308 uppers come using that gas tube. From what I understand the Ar10 (and lr308?) tube is just a bit longer(maybe 3/8"ish)and should extend to the center or just a hair past center of the cam pin cut out in the receiver. Look at one of your ar15s and you will see that's where the tube ends on those. This seems to be common from what I have seen but I changed mine out. They can be a little tough to find.
 
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Some good points everybody is making. Thank you!

It is a DPMS Gen 1 upper with a Young Manufacturing Carrier with a JP bolt/Cam pin running along inside.

I suppose i should have a look at the OEM DPMS BCG and do a little better side by side comparison.

I have a Kreiger barrel and have run into some accuracy problems.... I have no doubt the issues are rifle related.

What do you fellas believe the minimal gas block/Hand-guard clearance should be? I estimate clearance to be at least the thickness of 2, one dollar bills.

V223, what would be the advantage to swapping out to the appropriate gas tube? This model came with a 16 inch barrel and a carbine tube.



 
I like to see enough clearance that if you give the forward most end of the handguard a bump with your hand that it doesn't hit the gasblock. That's probably in the .040" neighborhood.

Honestly, I've only dealt with the rifle length gas systems on the lr308 platform. I'm not sure what the shorter lengths are gonna be.
I was fighting a cycling issue with mine. I was afraid the very minimal gas tube to gas key engagement was causing as issue. Not to mention the extra blast of gas into the area where the spent case was being ejected.
 
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Last night i believe i found the culprit for the receiver gouging. I pulled out the OEM cam pin and put it side by side with the JP. The JP is rounded only in one direction, squared in the other, and the OEM version is rounded front and back. I think the squared portion of the JP cam pin is gouging the receiver during the ejection cycle.
 
Interesting. AFA the gas block clearance, I'd personally want a good bit more. It also would depend on how much the barrel can flex, but if I could physically make the two touch, I'd feel pretty certain they would make contact during firing, and that can't help accuracy.
 
Originally Posted By: arlaunchLast night i believe i found the culprit for the receiver gouging. I pulled out the OEM cam pin and put it side by side with the JP. The JP is rounded only in one direction, squared in the other, and the OEM version is rounded front and back. I think the squared portion of the JP cam pin is gouging the receiver during the ejection cycle.

begs to wonder if putting the cam pin 180* orientation from its current would make a difference.

might want to contact JP about that. i'm sure they have an answer one way or another - even if that answer is "wow that one got past QC, let us send you a new one"

as for handguard clearance ... i'd want at least a business card thickness in there minimum.
 


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