Hi guys, any help will be greatly appreciated.  I have a 16" A2 Bushmaster that I recently decided to replace the upper on with a flattop.  i ordered a DPMS upper from the great guys at Del-Ton(super friendly).  I used the bolt and carrier from my Bushmaster upper in the new one.  

My problem is with the gun cycling the rounds, it will shoot a round and eject it fine but it won't chamber another one.  If I do it manually with the charging handle it will eject and chamber fine, it's just when I'm shooting it that it malfunctions.  I am newbie at working on AR's, is this a easily remedied problem or something I need to let a gunsmith look at? I thought maybe the bolt wasn't coming back far enough but I wasn't having any problem with my other upper.  
I also mounted a Surefire M97 light on the bottom of the gas block, is it ok to leave it there or does it need to be mounted to the forearm?  Thanks for any information you can give.


Jamie

BUMP

I am NO expert. That said, first off I think you should put the bolt and carrier from the Bushmaster BACK IN the Bushmaster! And get a new one for the upper. After a wile the bolt and the barrel sort of mold to gather. I can't really explain it but I am sure an expert will be here soon to explain all of it to you in fine detail!

Sounds like a gas problem.  Check the two screws that secure your gas neck to the bolt carrier.  Make sure they are tight and the gas neck is tight against the bolt carrirer.  If that is good, it is your new upper.  Port>gas block>tube is the issue.

Hey 50UNIT that was he problem I appreciate it bro.............thanks, Jamie