How many rounds fired in the rifle? What kind of ammo?  How's the chamber?  Do you have a chamber brush and give it a good scrubbing?  Carbon and crud build up?

Shot any steel cased ammo in the rifle?

How many rounds fired in the rifle? What kind of ammo?  How's the chamber?  Do you have a chamber brush and give it a good scrubbing?  Carbon and crud build up?

AR Bolt sticking,

So i hav e a new never fired AR, It was functioning fine when i put it together, Now i tried to cycle it with some plastic rounds (snap caps?) and the bolt is sticking failing to pull back and eject the round, Any ideas ?

 

Reading comprehension, FAIL.

 

How many rounds fired in the rifle? What kind of ammo?  How's the chamber?  Do you have a chamber brush and give it a good scrubbing?  Carbon and crud build up?

Regardless if it's brand new (assuming from MFR), I was wondering about the chamber condition and cleanliness as well.  Most of the MFRs test fire their complete uppers and I've heard that some sort of grease or other corrosion inhibitor all over.  The grease/corrosion inhibitor experience is second hand for me, but I've heard many reports to the effect that many caution to give the chamber and bore a pass or two to clean when they receive.  I've not personally done that for any of my guns and I've not noticed anything in the chamber or bore other than some mild carbon from test firing.

T'were me, I would chamber a round or two very slowly, feeling for any bumps or dragging as the bolt goes home and the round chambers.  Might illuminate where it sticks on the extraction.  Letting it slam home overrides any resistance with spring assistance, not present on extraction..

I like pressing the bolt into battery with my thumb, upper disassembled.  You can feel any rough spots, same with pulling the bolt back with the charging handle and not fighting the spring.  I like feeling the parts move.

That's kind of what I was getting at since I can't quite envision what he's describing as the symptom.  That I was just throwing stuff out there.  I have heard where people have installed the buffer tube and buffer retainer incorrectly and it causing some function issues, but since it's intermittent, I wouldn't think that this would be the case here.  Just sort of BSing here and throwing stuff out there since this issue sort of has me 

Try a different bcg?   Look for brass or plastic fragments that might cause sticking?