This is my first build,
DPMS lower,New
Dpms upper complete 11.5 with 5.5 FH, New

Having a short strok problem, Can't fire more then one round.
Went to the range to test fire and it started on the first round, Sometimes it will throw the casing and not feed the next round, but most of the time will not throw the casing. I have switched the bolt and carrier to my other AR and it works fine, I have taking my old bolt and carrier and put it in the new upper and the same thing happens, I have switched lowers, upper,bolts and carriers and the problem seems to be the new upper. Does not seem to matter what ammo I shoot (Wolf or Win) Everything works in my old AR, It's a DPMS with a 16 inch barrel. I am new to the AR world and need help, I have read some stuff on short stroking and am totaly confused on what to do. I have done the single shot thing with the mag and the bolt does not catch, Bolt is not going back far enough. I have a gas problem and I'm not talking about my body. Please Help. I am calling the place I got the upper and see what they say. Thanks Dave

Is it a used upper?  Have you pulled the front sight base and cleaned the gas port in the barrel and the FSB?  Get a new gas tube as well.

Randall

Okay, you've swapped bolt carrier assemblies and lowers, and it still short strokes. That narrows it down to the upper receiver then, as it is the only constant part in your malfunctions. Some things to look at are:

1. Inadequate lube.

2. Obstructed barrel port or front sight base.

3. Rough chamber.

Tell us more about your rifle. Is the upper factory or home-assembled? Does it have a standard front sight base or a gas block?

Those 11.5" barrels are notorious for short stroking...

If you determine that there is no gas leaks or obstructions causing the problem, you will probably need to open up the gas port... If the gas port is under .086" then it will definitly need opened up a bit... Usually opening it up to around .090" - .094" will do it... Don't go the maximum right off the bat... You want to ream it in .002" increments starting from its original size until you reach your goal...

Upper is brand new DPMS factory. Not sure on the gas leak. I don't want to screw it up, I think I will return it and get a different upper that works right, I have only owned AR's for three months now and am still learning. I would think that they test fire the upper before it leaves the factory (maybe not)How can they let a upper leave the factory that only shoots one shell at a time? Sorry just frustrated. Do you think a hotter load would help? Thanks for the help guy's. Dave

Like others have asked...Front sight base, or gas block?  Either way, check to ensure the roll pin is in there to hold the gas tube in place.  I've seen multiple AR's short stroking, and more often than not, this is the reason.

I have a front sight base and roll pin is there.

Removed the FSB and gas tube, All looks good, Going to the range today with some hot loads.

Thanks Dano523, I will do that