ar wont send

[im2old]

I just purchased 2 ar uppers at a pretty good price. I THINK.
The first one will eject fine but wont throw the next round home, and the second one wont eject. The second one will come back half way and jam, but, its not hard to to pull back to eject the round. Sometimes it will eject but, will only send the next round half way in.
I'm using a bushmaster lower and have no problems with the Bush upper at all.
All 3 barrels shoot 1/2 in at 300 yards on a low wind day with the 45gr. hp.
What might be the problem with the 2 I purchased? Or was I just a big  lollypop. :?
I have 11 different mags of all kinds and the problem EXSISTS with all of them.
Any help would be gratefully apprieacted.

[gunnut69]

The first one ejects but won't feed?  It jams the round being loaded or closes on an empty chamber?  Won't close all the way?  Is the round holding the action open.  Sounds as if you may have a low gas pressure problem.  Crud in the gas system, burrs on the bolt assembly, not lubed?   Check the bolt head and the barrel extension for burrs/casting flashes.  Clean the gas tube and would probably be a good idea to clean the entire upper.. Be sure to check piston clearance in the cylinder..  Were these new uppers..

[im2old]

I've cleaned and checked for burrs same thing.
Should I purchase new tubes??
Are all tubes the same length? The one that ejects but wont throw another has the standard ar sight and I put a new tube in when I cleaned it the first time. The second one that wont eject I put a new gas block on and I did notice the powder marks were on only half of the tube hole.
Ill have some one mill the gas block off.
Does the hole in the tube have to be excact?
Thanks Sorry bout the questions, never had the problem in the last 25 years. :?

[gunnut69]

The gas tubes do differ but only between certain variations.  The CARs have this problem and it's solution is a pigtail gas tube.  Evidently the length of the tube has an effect of the duration of the gasses push on the piston..  The gas tube should deliver all the gas tapped from the barrel..  It surely sounds as if you are having short stroking problems and that many times is the gas system, expecially since the lower works with another upper.  Check for drag or bind marks on the bolt carrier and be certain the bolts are cleariong the ammo in the loaded mags.  My guess is a gas problem...  the ar's are fond of such things..

[im2old]

will look in browns, and again thanks for the help