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Capita159
07-24-2011, 2:26 PM
Check this out, I've search over the internet and CGN but couldn't find an answer to resolve this matter. I not 100% sure if this is an major issue. But it does scares me. The rifle is a CMMG MK8 lower with a JD Machine matching upper to accept G3 magazines, and the rest of the main components are DPMS, such as the BCG, barrel, LPK, and complete 308 rear stock. The rifle functions fine and sheds no issues other than damage on the buffer. I mainly shoot 175gr ammo.

From what I've experience, this is a common issue. What I like to know is what parts can be change to prevent this from happening? Any input is appreciated, pictures below.

http://farm7.static.flickr.com/6143/5971796540_36eb7e6a9a_b.jpg

http://farm7.static.flickr.com/6009/5971244417_f075ab644f_b.jpg

http://farm7.static.flickr.com/6147/5971248609_2992ab1199_b.jpg

crazychinaman
07-24-2011, 3:07 PM
Are you using the right buffer and spring.? .308 AR use a longer spring and should use a heavy buffer.

Len
07-24-2011, 3:07 PM
Not heavy enough buffer spring or its wore out.

Capita159
07-24-2011, 3:24 PM
Are you using the right buffer and spring.? .308 AR use a longer spring and should use a heavy buffer.

Yes, the complete stock kit is from DPMS and is for 308s. I am going to try a longer and stiffer spring. The buffer is a 308 rifle buffer and is at 5.4oz. Pretty standard AR rifle buffer weight. I currently can not find a heavier 308 buffer.

Not heavy enough buffer spring or its wore out.

I have a longer buffer spring. The thing is, it has seven coils less than the 308 spring, yet an inch longer. I think I going to have to call Midway are Fulton to see if they have anything stronger than what I have.

Thanks for the replies :)

Dan-0-
07-24-2011, 4:07 PM
I am curious to know how many rounds caused this and if you purchased all your components brand new or second-hand.

greybeard
07-24-2011, 4:10 PM
Is it a A2 stock or carbine one?

atv
07-24-2011, 4:28 PM
Here is a pretty handy table of buffers and springs, are you sure you are using the right spring, or right tube length?http://tapatalk.com/mu/ad0883e5-aa83-5816.jpg

FatalKitty
07-24-2011, 4:40 PM
looks like it's hitting the retainer pin... but the BCG should keep it from going that far...

VytamenC Tactical
07-24-2011, 4:44 PM
looks like it's hitting the retainer pin... but the BCG should keep it from going that far...

+1 looks like that is exactly what is happening

Capita159
07-24-2011, 5:32 PM
I am curious to know how many rounds caused this and if you purchased all your components brand new or second-hand.

I've put about a 1000 rounds through the rifle. The stock has been on the rifle since day day. Everything on that gun is bought brand new and the upper was assembled by Randall.

Is it a A2 stock or carbine one?

A2 stock for 308.

Here is a pretty handy table of buffers and springs, are you sure you are using the right spring, or right tube length?http://tapatalk.com/mu/ad0883e5-aa83-5816.jpg

That is an excellent chart. Looks like a have a 39 coil spring for my 308. If that chart is 100% correct, I am using an AR15 carbine spring lol. But I do have a 34 coil replacement spring that is 13.5" long. That might be the best and correct spring to use on my AR308. :D Thanks again for the chart. I saved that Jpeg for future reference,

looks like it's hitting the retainer pin... but the BCG should keep it from going that far...

Yes, it's pretty obvious. The retainer is fine and there is no sign of wear in the carrier. I think I am going to have to modify the lower receiver to match the upper better.

bohoki
07-24-2011, 5:33 PM
+1 looks like that is exactly what is happening

yep looks like its hiting the pin

did you install the barrel to the upper

you can shave a bit off the front of the upper where the barrel shelf mates to bring the bolt carrier back

or just get a new buffer and run it without the pin

pyro3k2
07-24-2011, 10:27 PM
I would like to see a picture of the detent it was hitting against I would imagine that may need to be replaced as well.

FatalKitty
07-24-2011, 10:40 PM
actually the pin is probably fine... maybe a little bent.

the problem is that the buffer is coming too far forward, either because of a bad fit between the upper/lower - or it's a barrel/carrier issue.

pyro3k2
07-25-2011, 12:51 AM
actually the pin is probably fine... maybe a little bent.

the problem is that the buffer is coming too far forward, either because of a bad fit between the upper/lower - or it's a barrel/carrier issue.

I'd still like to see a picture of it.

Capita159
07-25-2011, 2:16 AM
FatalKitty is correct, the retainer pin is a little bent, yet not really noticeable until it is removed from the lower. And yes pyro3k2, the retainer pin should also be replaced.
I am now 95% convinced that the retainer pin hole needs to be moved forward about 0.01-0.001 of an inch. This should solve that buffer problem.