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8/22/2014 4:37:15 PM EDT
Hey Guys i just finished a AR15 Build
CMT Upper
Seekins 223 Lower
Rainer Arms BCG
Ballistic Advantage Barrel
YHM Gas Block

The first 2 rounds fired and 3rd did not cycle. After that it would just start shooting singles and would not chamber the second. I was shooting federal 223, tula steel case 223...
I also shot 5.56 and worked fine.

My friend was there with his ar15 and we swapped uppers, mine worked with his lower and his worked with my lower.
We also tried his bcg in my upper and also worked fine.

What else could it be? what should i check?
8/22/2014 6:00:56 PM EDT
[#1]
If is not cycling than gas block can be lose or misaligned. Can you move bolt back with empty mag and lock it up?

Do you have correct spring for your buffer? Put the tubing on  the end of gas tube and blow; it shouldn't be much resistance
8/25/2014 11:59:37 AM EDT
[#2]
if you swopped out and used his bolt carrier group and it worked fine i would say that kind of narrows it down a little unless it was a fluke

it the bcg brand new?

did you lube it ?

check the Gas rings

and is the key staked properly I would assume from RA it would be .  But weirder things  have happened I had a AA grendel that had a out of spec gas key that caused feed problems I had a spare and the problem was solved

odd you switched lowers and it worked. did the problems start when you used tula like used tula for your rifle then switched lowers and used federal .

and when you tried his bcg was it on his lower? You got a lot of mixing going on .

I suggest checking your rings to make sure they are spaced correctly , lube the heck out of it  make sure key is tight and staked  . make sure you have the right buffer spring and its working correctly check the alignment of your gas port and gas tube and leave the tula at home until you figure it out.

typically and most often this problem is related to the gas block or gas key  but you are either not getting enough gas or loosing gas or binding
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