View Full Version : 9mm AR Help!

We The People Firearms
09-06-2010, 8:57 AM
Just got done with my 9mm AR. CMMG Upper, LRB lower. Forgot about the pistol caliber weight buffer. It fires one round, then the bolt carrier is extremely tough to draw back. Totally stuck. Had to take it apart many times. When I did get it apart, the spent casing was still attached to the bolt face. Does the extra buffer weight keep it into battery long enough for the round to completely discharge? Can a standard carbine recoil spring be used? I have a dedicated 9mm hammer, everything else is good. I'm hoping it's just the buffer. Thanks

09-06-2010, 10:21 AM
Is your bolt ramped? If so you are supposed to use a standard 5.56 hammer (you probably know this though). Not sure if that would cause this problem, but just checking. I have the buffer and spring but a RRA upper, some people find they need it while others don't. I would say start there, pretty easy to figure out if it's your upper at that point then.

09-06-2010, 12:38 PM
I have a spikes 9mm upper. I use a standard AR hammer. You need the heavy 9mm buffer and the additional buffer insert that goes at the other end off the buffer spring. I have no problems.

consider this option..


09-06-2010, 12:59 PM
I have a RRA upper with spikes 8.5 oz buffer with standard carbine spring and mine runs like a clock. over 1000rds with NO malfunctions. Buffer weight is really critical in a 9mm because of it being direct blow back. try a 9mm buffer and spacer as suggested above and you should have good results. Also if your is a complete CMMG upper you need to swap out your 9mm hammer for a standard hammer.

We The People Firearms
09-06-2010, 3:33 PM
I have heard that a lot of people don't use the 9mm hammer. I can switch that out. Is the heavy buffer to reduce recoil, or to keep the bolt engaged longer? My gun isn't even cycling. The bolt goes back about a 1/4 inch and locks up completely. Have to bang it and rip the charging handle to get it to open. I would think a lighter buffer would just let it cycle faster. Thinking it might be something else??

We The People Firearms
09-08-2010, 7:48 PM
I think you saved me. I looked at the wear on the 9mm hammer, and it is torn up on the center notch. This would explain it locking up. Switched hammers, just haven't founf a "quiet" place too test it. Thanks. New buffer on the way as well. Can a spacer be made from a piece of polymer? Dimmensions? Thanks.

09-08-2010, 8:03 PM
Your CMMG doesn't need a 9mm hammer, got one myself. You do need a heavy buffer as xbimmers said.

big ron
09-08-2010, 8:12 PM
Your CMMG doesn't need a 9mm hammer, got one myself. You do need a heavy buffer as xbimmers said.
x2 and no need for a spacer if you are running a carbine stock.

09-08-2010, 8:23 PM
Ya, the spacer some are talking about is for a fixed stock if you are running that, otherwise the buffer and spring (yours may not even need these in all honesty but I would say get them) as well as a standard hammer and you should be good to go. Check your bolt though because there are some CMMG's that aren't ramped, but most are. Sounds like you targeted the problem and yours IS ramped.

09-08-2010, 8:30 PM
if your using a carbine length buffer tube/ you don't need a spacer- spacers are for rifle length stocks/ tubes with carbine length 9mkm buffers.

if you're using an A2 stock and tube / you can get away with the standard rifle buffer.

We The People Firearms
09-09-2010, 10:15 AM
Thanks guys. Changed the hammer and all appears to be well. Except for the crappy Pro mags that the lips broke on.