Hello guys , I took my DPMS AR-15 low-pro  out to the range for the second time since new . First time out , I took the time  and broke in the  barrol ( I cleaned between each shot for 25 shots found out later may not have been needed ). This time out , after 40 -50 rounds , it would shoot the fist shot , then not load the next repeatedly. The range officer  who has a bushmaster said "not loading the second shot is a common proplem with AR's   " he suggested I try other ammo which I had , then tried a diferent clip ( plastic ) then a metal one ( just got it's a 20 that only holds 10 ) than was worse , then take off the brass catcher which I did , then he said to take it apart clean it and don't over oil it . I have not shot it since cleaned and lite oil job , but I wondered what you guys thought !  Thank you !                   John Martin

Quoted: The range officer  who has a bushmaster said "not loading the second shot is a common proplem with AR's   " he suggested I try other ammo which I had , then tried a diferent clip ( plastic ) then a metal one ( just got it's a 20 that only holds 10 ) than was worse , then take off the brass catcher which I did , then he said to take it apart clean it and don't over oil it . I have not shot it since cleaned and lite oil job , but I wondered what you guys thought !  Thank you !                   John Martin

Whats that thing shoot, paper clips? I prefer the metal ones over plastic... Hey, does it have a rubber band too?

given it seemed to work okay for close to a hundred rounds, the comes up short... I would suspect that it developed a gas leak?

Check that the bolt key is tight... look at the gas rings, and make sure that the FSB/GB is where it is supposed to be, has not creeped forward or turned if it can...

let us know, okay?

Getting back to your problem... You could have a gas leak... Most leaks are caused by improper seating of the carrier gas key... Its possible that the gas key screws are loose or the area where the gas key/carrier surface meets is out of spec and not matching up properly to make a tight seal...

  Broke it down tonight , took off scope to get gards off , nothing loose by hand , there is witness mark of movement at the top ring that holds front of gas tube , don't have all key to take apart further . I did clean the gun with some spray bore gun cleanner . messed up the teflon up pretty good so it probably got the dirt out hinking.gif
   If it improves with the cleanning , I will let you know .  

Did you clean and oil it before the first trip to the range?

I had a buddy who bought a Bushmaster M4 once, then took it straight to the range.  On the second trip, he developed exactly what you're describing.  I broke it down, oiled the carrier REALLY WELL, then put it back together.  Never another malfunction.

I really wonder if you haven't under-oiled it for fear of over-oiling it.

I had the exact problem on my first AR (a Bushmaster 16" preban). I concur it is a GAS LEAK. Probably from the bolt carrier/carrier key.

Mine started doing it after I shot my first 1500 rds of Wolf Ammo. I started reading about it and everyone was bad-mouthing the Wolf Ammo saying how it is dirty shooting, gums up the gas system, gums up the chamber with laquer, making rounds stick, delaying the extraction, short cycling, not picking up the next round,...blah..blah...blah. (sound familiar??)

I was pissed at myself for buying cheap ammo in order to shoot more and increase proficency. (not a high point for me) and I went 6 months to a year without shooting it (work/family does get in the way!)

Did all the cleaning/ oiling (but not over-oiling), mag swaps, ammo swaps. Nothing.

Broke the rifle down TWICE. Meaning down to the individual pieces. (ie gas block off the barrel cleaning with pipe cleaners). Took a chamber brush and my Makita to the chamber. Nothing!

Looking at the carrier and carrier key I could see that the Allen head screws on the top were staked in as they should be, and there is NO WAY they could have backed out........WRONG!!!
I put an Allen wrench to them and they spun freely! So I removed the key and checked the mating surfaces of the carrier and key and found streaks of carbon where gas had been escaping.  Gas escapes, delays unlock, bullet exits barrel, gas pressures go down=short cycle!

See this manual posted here (http://www.ar15.com/content/manuals/TM9-1005-319-23.pdf) and look on page 265 for a good shot of the Carrier and Carrier key.

I cleaned the surfaces and went over them with some steel wool just to make sure. Put a fine thin (barely visible) coating of Moly Grease on the surfaces, put the key back on, and torqued the shit out of the Allen screws.

That was 4 years ago (and 5 AR builds ago which taught me alot too) and my Bushmaster runs like a sewing machine!!! It never hiccups and it'll eat anything!!

The AR is a great rifle and will function as advertised. If it doesn't, the problem is easily fixed due to the modular design. Just find a manual and run through a troubleshooting checklist. There was a discussion on another post about whether the AR was "built" or "assembled"
by the homebuilder. I think the beauty of it is that its assembled and can be serviced by the home user easily.

Hope this helps!

SnowFAL

Hope this helps!!