I just completed a new build and am running into problems.  Sorry if this is a bit long but I want to explain fully what I'm seeing.  Here are the components

18" Rainier Ultra Match Barrel
WMD M16 BCG
VLTOR MUR-1A Receiver
Troy Low Profile Gas Block
Gen3 20 Round PMAG

Other components which may not be so important

Mega Billet Lower Receiver
Geisselle High Speed DMR Trigger
Magpul Fixed MOE Stock
Rifle Buffer Tube, Buffer and Spring
Samson Evolution Free Float Rail

I tried to shoot in for the first time today.  After firing the first round the second round loaded, the bolt rotated shut and the bolt carrier group failed to go fully forward into battery.  I tried pulling the charging with a great deal of force to extract and wasn't able to.  I fiddled with it for a while and hit the forward assist about 10 times until it eventually went into full battery.  I removed the lower and inspected the upper.  I was able to get it to pull slightly out of battery and then push the forward assist to move it forward.  After reffing on the charging handle for a while the BCG eventually flew out of the upper and onto the ground.  

I inspected the bolt carrier and relubbed it with CLP.  It was already properly lubbed intially but I figured it wouldn't hurt to add more lube.  I shot it a few more times and after about 20 rounds it seemed to function more consistently.  It however fails to go into battery about every 5th round.  Extraction of a round is also more difficult then what I've seen on my other rifles.  Inspecting the fired casings shows the extractor is chewing up the rim quite a bit.  

So what do you guys think?  I'm leaning towards the receiver being out of true but that's just an initial thought.  

Reloads with the die adjusted incorrectly.
Or need to check for adequate head space.

Factory Ammunition
Federal 223 from Walmart 100 Packs &
Hornady Steel Match 75 Grain BTHP

Headspace was checked
Closes on go gauge but not no go gauge.  Checked with extractor and ejector removed.

I'll try this out this evening.

I removed the bolt and it does not appear that the gas tube is interfering with the gas key.  I cannot visually see it but I can close the carrier all the way into battery with no resistance.  

I installed the bolt and dropped the bcg into the receiver and it closes.  I can move the carrier back with my fingers with little effort and the bolt with rotate freely in the barrel extension.  

When I was at the range I had the bolt hold open 4 times on an empty mag.  No failures to hold open on an empty magazine.  The brass that was fired was found 10-15 feet at 4-5 o'clock.  

So...  Looks like a problem with the ammo then.  I'm a bit surprised as it was two different types of ammunition it had problems with.  One was much worse than the other however.  Maybe I should do a good cleaning with a chamber brush.  I'm a bit surprised however since it's a brand new barrel.  Do some ARs have a break in period?

You might have an undersized chamber.  Pictures of the fired cases would help.  It is POSSIBLE the chamber reaming was done with a rougher (undersized) reamer and somehow missed the finishing reamer process.  Yes, it is possible for correct headspacing with a roughing reamer.



This would explain the tight chambering and hard extraction.  The fix is a trip back to the manufacturer.  You could try making a chamber cast with Cerrosafe, a low temperature melting alloy which shrinks upon solidification for ease of removal but slowly recovers dimension over time.


 

I unfortunately didn't keep the brass that I fired.  I'll shoot it some this week and if it is still having problems I'll post some pictures of the brass.  

Went ahead and cleaned the chamber.  I'll try it again this week.  This is a 3 gun build so it looks like I'll be running my BCM 16" until I put enough rounds through this one.

Well after cleaning the chamber with a chamber brush it fails to go into full battery consistently.  Failure happens about 1 in 20 with federal brass and about 1 in 5 with Hornady steel match.  Looks like the barrel is going back.  It's a real bummer.  Now I have to decide if I should wait for a 18" BCM barrel I would ultimately like to have or spring for a WOA 18" DMR that is available.  Decisions....

I had this exact thing happen to me. For me the extractor was too tight and could not get around the rim of every 8th round, chewing up the rim quite a bit. What ended up fixing it for me, as another poster mentioned earlier, was to remove the o-ring around the extractor spring. It is a very simple fix. If your bolt does not have a an o or d ring then you may just need a new extractor or extractor spring. Try the extractor before you blame the barrel.

Also, a close up picture of your bolt face could help determine if it is the extractor.

I must have overlooked that suggestion.  Another reason to go to the range.  Perfect!  

The bolt did have an o ring.  I removed it and might go to the range later this evening.

Great! I hope it fixes it for you. I know when my rifle was doing this I was so frustrated that I could hardly stand it.

Good luck! Let us know if it fixed it!

Well that did the trick.  Ran 50 rounds of the Hornady steel match without a problem. Totally makes sense why this would have caused the problem.  Some pictures of the gun and some groups.  




Not the best shooting.  I blame it on the weather  Thank you everyone for your help.  

Holy cow.  Glad I stumbled onto this thread.  I was surprised by the fix.  Another good to know tidbit to check if similar issues appear in my AO.

Nice rifle! Love the grey barrel on the black rifle. I did the same on mine.

Appreciate it!  Thanks!