Hava a brand new ar15 that was put together. Shot the first 50 rounds through and had no issue at all at the range. Went last weekend and the empty casing kept jaming every third or fourth shot. I was using PMC 223 55 grain ammo with magpul 10rnd mags.  I'm a noob with the ar15 and have no idea why it's jamming....

Here's my build list if it might help
Lower:

-JL Bilet AR15 80% lower (170)
-Rock River lower parts kit with single stage trigger (67.95)
-MAGPUL ACS-L Mil-Spec Adaptable Carbine Stock (84.95)
-Mil Spec 6 position Stock Hardware Kit (42.95)
-Assault Planet Bullet Button (18.95)

Upper
-Spikes Tactical Barrel ST-16" 5.56 1/7 twist (199.99)
-Yankee Hill Machine Rifle Length Lightweight Free Float Rail (119)
-CMMG Gas Tube (15.95)
-YHM Low Profile Gas Block (22.95)
-Rock River Arms -A2 Flash Hider (7.50)
-JoeBobOutfitters Premium Complete Bolt Carrier Group and andronized charging handle (129.96)
Vortex SPARC Red Dot (199.99)
Upper: MEGA Forged Stripped*M4 Upper - A4 (114.00)
Upper Parts Kit Rainer (24.00)

There is a problem with your ejector or/and extractor.  First check to see that the ejector pin is able to move pushing on it with a brass punch.  This should take some good amount of pressure but feel smooth.  Next look at the extractor for any inconsistencies, a good edge, strong spring tension as well. Probably a good idea to take the bolt apart and take pictures of this stuff to post here if insure.  I am not familiar with the quality of Joebob's so this is my suspect.

While at it with the rifle assembled, pull back on the charging handle as far back as it goes. Look to see where the bolt face stops near the rear of the ejection port. If it retracts past the rear I the port more than 1/8" take out the buffer and spring and place a quarter in the bottom re-install the spring and buffer so the bolt face is near flush with the rear of the ejection port. This is a bandaid fix for the extractor and ejector not working correctly.

thanks guys, gonna take a glance at it tomorrow so I can go shooting this weekend. Such an annoying issue lol.

where did you learn that I have never heard of that quarter trick before was that from some thread or just a range fix ?

Heard it here at Arfcom. And have done it to keep my carrier key from slamming against the receiver extension ring in one of my rifles

A couple other things to check-make sure your gasblock is tight and has not moved. I had one customer who brought in a rifle that was acting similar. Hella bitch to find the issue but he had not LocTited the setscrews for the gas block. Every couple of shots it would work forward just enough to partially block the gasport causing the rifle to short stroke and stovepiping the casing. When he was clearing the jam he would pogo-stick the rifle on its butt causing the gasblock to slip back into the correct position and it would shoot fine for a couple shots then do the same thing. Spotfaced where the setscrews went, red LocTite and off to the races.
Also check the orientation of the gasblock/gas port holes. I had a rifle come in that was inconsistent and after pulling the gas block the problem was clear, the hole in the barrel was fine but the one in the block was off center due to a manufacturers defect. Only about half of the hole lined up. Corrected the hole in the gasblock and she ran fine.

I have also seen 2 brand new bolts with burrs in the ejector bore that kept it from traveling freely.

I swear, I have seen more QC issues with components in the last year than I have ever seen.

Some industry partners were just talking about this a few weeks ago here on arf.  They have seen an increase in material and non-house items not being up to snuff trying to get enough out to meet the demand.

Panic buying causes QC to lapse. Happens everytime there is a rush on the market.

We saw QC lapse with LMT & VLTOR during the 2008 panic buying.

Now we are seeing it from Spikes, BCM, DD

http://www.ar15.com/forums/t_3_66/621873_New_rifle___rail_off_center___Send_her_back_.html

http://www.ar15.com/forums/t_3_66/621183_My_Barrel_is_out_of_alignment_with_rail_and_upper_on_new_AR_build___Please_help_.html

http://www.ar15.com/forums/t_3_66/620997_Daniel_Defense_m4_v7_issues.html

http://www.ar15.com/forums/t_3_66/620260_Small_chunk_missing_out_of_Bolt_Carrier.html

http://www.ar15.com/forums/t_3_66/613248_New_DDM4v4_wont_hit_target_and_keyholing_when_it_does__HELP_plz__.html

Happens everytime there is panic buying.