We need more info, what ammo and mags was you using, it looks like you have a soft tip commercial .223 ammo in your pic.
I only have a small sample size of 6 Colt AR (4 rifles and 2 carbines) that I used to own from 1971 up to 2004, currently since 2005 and on I've got 4 Colt, an older 6920 (2011), two 6721 HBAR heavy barrel carbines, and a USGI M16A2 20" barrel upper half on Colt HBAR rifle lower with fixed A2 buttstock (and one 6920 M4 carbine 2012 configuration I gave to my son last month).
Mostly I use surplus M193 55 grain Winchester, M855 62 grain Federal, Canadian import SS-109, and various brands of commercial .223 from 50 gr up to 75 gr bullets, full metal jackets and hollow points (I don't use soft point bullets) no problems.
I only had one occasional feeding problem with surplus Winchester M193 55 gr Q3131 ammo and a bad Colt 20 round factory mag on a 20" HBAR heavy barrel (with approx. 600+ rounds fired), the main cause was an out of spec mag.
This almost same as your problem happened on my other LMT 16" M4 type carbine with a semi-auto bolt carrier and standard weight buffer with USGI 30 rd and PMAG gen 1 magazines,
I changed my complete BCG with LMT M16 full auto carrier, upgraded the bolt extractor spring with a extra power BCM spring upgrade kit (did not use the O-ring), changed the buffer with a LMT H heavy buffer and the problem went away.
Try cleaning the bolt group and extractor, feedramps and chamber well and lube it with good synthetic lube, I use SLiP 2000 EWL, lube it shown in the below link.
Also try other mil-spec 5.56 ammo and full metal jacket bullets commercial .223 loads, also try other magazines.
http://www.ar15.com/forums/t_3_7/548967_AR15_LUBE_POINTS.html