View Full Version : problem with 6.8MM upper

12-17-2008, 4:50 PM
I have a 6.8mm that i recently purchased and when I pull back the charging handle it crushes the buffer detent and spring under the detent (well bends it good) the upper says 6.8 MM and lower is stamped 5.56. The upper and lower are brand new the upper i think is bushmaster and lower is RRA anyone have advice?? thanks

12-17-2008, 5:02 PM
sounds like the recieve extension is not installed all the way in and is allowing the buffer stop and the spring to rise up into the bottom of the bolt when its cycled. Make sure that buffer stop is contained by the reciever extension being all the way in and covering the shoulder of the stop. Then it can't hit the bolt.....just my thoughts.

12-17-2008, 5:12 PM
tried humm i only have 2 parts kits ant this upper is destroying these buffer retainer and buffer retainer spring :(

12-17-2008, 6:15 PM
Can you post a pic?

12-17-2008, 6:18 PM
should look like this.


12-17-2008, 6:23 PM
"sounds like the recieve extension is not installed all the way in"

I am not familiar with the term receive extension but It sounds like what I was thinking which is the buffer tube is not threaded far enough in to prevent the buffer stop from rising in the way. Vinz has a good picture of how the buffer tube should look and how close it should be to the buffer stop to engage it.

12-17-2008, 6:38 PM
Your right, it was spelled wrong, it should read "reciever extension" as its listed in parts diagrams and on sites like rifle gear and midway. But yes were describing the same thing.

12-17-2008, 7:04 PM
The proper term for the "buffer tube" is the Receiver Extension.

It does sound like this is the problem which is why I was asking the OP for a pic.

12-17-2008, 7:17 PM
Do you by chance have an A2 type stock with a sling adapter installed? If you can answer yes...........pitch the sling adapter. Ask me how I know.:kest: