Just got back from the range for the first time shooting the AR I built. Having an intermittent feeding problem. Sometimes it will run 30 rounds with no issue sometimes it jams every round. Tried with a brand new pmag and a used mil mag.

Rifle was cleaned and lubed before firing.

Check the gas block alignment...if it doesn't blow the carrier back far enough it will do exactly what your picture shows. Also make sure your feed ramps match your bbl extension/lower combo

Looks to be short stroking. What kind of ammo?

Hornady 55gr HP and Winchester RazorBack XT 64gr. The RazorBack actually ran with no issues, but I only shot 10 rounds. I shot 50 of the Hornady.

Are those Hornady rounds the 50 round packs of "training" brass ammo they make? I have been told many people have problems with that ammo due to it being underpowered.

If not, check your gas block alignment. It's possible you don't have it on there quite right.

Who built the rifle?

I built it. I've got some other ammo, I'll do a little research on the hornady and shoot something else to confirm before taking it to a gunsmith.

YHM lower
DPMS parts kit
Magpul Grip
Magpul MOE stock + Larue milspec buffer kit
Bravo Upper Receiver
Bravo 14.5 Barrel
YHM Flash Hider

If you built it what do u need a gunsmith for? Check your gas block alignment.

Is that a live round being fed in or a fired case that was not extracted?

Just want to confirm-you started with a stripped upper and barreled it yourself or you assembled a lower and installed a complete purchased BCM upper?

What buffer are you using?

X2, what weight?

Unsure about the buffer weight. It is the one from this kit. I believe it is the milspec which would make it 3.9?
http://www.laruetactical.com/combo-magpul-ctr-mil-spec-stock-and-receiver-extension-kit

Bookxvt and Corelokt - yes

What exactly is happening?

Is the spent round being extracted? Where is it going? (forward, 90* or back?)

Is the next round jamming in like that?

any scratches on the case of rounds that are feeding ok?

My vote is that you check the following:
- gas system alignment
- buffer weight
- buffer spring length/strength (on my 14.7" AR I had to swap to a slightly shorter buffer spring to reliably fire steel ammo [which has less gas because it doesn't seal the chamber as well as brass])

It could be the gas block not aligned to the gas port in the barrel.

Update: Fixed the issue. My gas block was a few hairs too close to to the muzzle end.

Some good info there.