The upper is a Bushmaster M4 with a 14.5" barrel, 1/9 twist. Fired about 100rds already with no problems.
The bolt carrier is a RRA enhanced bolt carrier assembly. Using Federal XM193 ammo. Tried different lots, same issue.
Wondering if anyone knows what is happening, as I have never seen this type of problem.

When I fire the weapon, the empty shell gets slammed in between the bolt & the chamber, and doesn't quite get ejected.
The shell is half in & half out of the ejection port with the ass end inside and the empty end pointing straight out the ejection port.
The next round loads into the chamber ok, but the empty round doesn't make it out of the ejection port.
I took the weapon home, cleaned it, and took the carrier assembly apart to inspect & clean it as well.
The bolt looks fine & not really dirty at all. The bolt was a little sticky inside the carrier, but nothing visibly wrong with it. I took the carrier key out, and pulled the bolt out & that is when I noticed a little stickiness.
But there is nothing on it. The carrier also looks fine too.  Anyway, I cleaned the whole thing and lubed it all with a light coat of CLP with my finger. Just a fine film.
Took it back to the range, fired one round, ok. . . fired another round and it started doing it again.
I tried the mag & ammo in another weapon. Fine. Not the ammo, not the magazine.

Sounds like the round is getting reliably extracted, but as you stated not ejected.  This may point to the ejector.  This is a spring-loaded round projection on the bolt face.  It will be along the inside wall of the ring created by the lugs of the bolt.  This should have lot and lots of force.  Should be almost painfull to try to push against it with tip of your finger.  With an empty case however, you should be able to push it down all the way and really feel the sping force it has.  If this is spring force is weak you may have a problem.  I think I know how to remove the ejector so you can check the components, but I've never done this so I'll have to defer this advice to someone who has.

BTW, Is there anything in the path of the ejected case?  A snap on brass-deflector or brass collector?  Scope riser with large thumb nuts that may be in the path?

Tex78

I'd check the extractor spring or the ejector. I'm betting extractor spring.

Sounds like what is happening is that the ejector is overpowering the extractor.  When this happens the ejector pushes so hard on the brass that the extractor can no longer hold the brass and lets go of it before the bolt moves far enough rearward for clean ejection.  You can remedy this by installing a Wolff XP M4 extractor spring.  Send me your address and I'll send you one free of charge.  You may also want to invest in a LMT H buffer (less than $20) from most LMT dealers, this will slow down the cyclic rate of the carbine and make your bolt last longer and your weapon will be more reliable.  The old fix before Wolff M4 extractor springs was to remove 1 to 2 coils from your ejector spring (I no longer do this).

Factory 'rifle' extractor springs are too weak for carbine use.  EVEN Colt has changed to stronger extractor springs on M4s.  M4s have a higher cyclic rate and have the extraction problems because the bolts on them start to open when the chamber pressure is still pretty high (higher than a 20" rifle).

Nothing in the way of the round ejecting. . .

Why would this happen all of a sudden?  I fired a few mags through it when I got it, to sight in in.
Then it has been in the safe for a few weeks or so. . . now today right off the bat, it has problems.
Safe is in a climate controlled area of the house. . . low humidity. not that it matters to a spring.

The bolt carrier assembly is also new, bought from Eaglefirearms.net
The thing isn't even broken in yet, you know. . .

gotm4 ~ IM on the way. . .

Thanks

Quoted: Nothing in the way of the round ejecting. . . Why would this happen all of a sudden?  I fired a few mags through it when I got it, to sight in in. Then it has been in the safe for a few weeks or so. . . now today right off the bat, it has problems. Safe is in a climate controlled area of the house. . . low humidity. not that it matters to a spring. The bolt carrier assembly is also new, bought from Eaglefirearms.net The thing isn't even broken in yet, you know. . . gotm4 ~ IM on the way. . . Thanks

It's because it actually broke in the extractor spring that fast.  May sound impossible but it's true.  My Bushmaster did it back in 1997 when I first built it within the first 100 rounds.  Back then the stronger extractor springs weren't yet available so I trimmed about 2 coils of the ejector spring off and it worked well.  Now that they are available I run a standard ejector spring, Wolff extractor spring and a PRI Fat Boy gas tube (with standard CAR buffer and spring).  On my wifes M4 I use a standard CAR gas tube LMT H buffer (standard buffer spring), Wolff M4 extractor spring and both weapons have been 100% reliable.  I recommend getting the H buffer as it's cheap compared to my $50 gas tube.  Both work well but the buffer is much cheaper.  I think G&R Tactical has the H buffers for $13  

Can you explain your use of the word extractor & ejector . . . I am not sure I understand what you are saying . . . well most of it I get . . .
Just not the difference between the extractor & ejector spring, because you say that your extractor spring broke but you trimmed the ejector spring ~ Typo?

Thanks . . . db

Quoted: It's because it actually broke in the extractor spring that fast.  May sound impossible but it's true.  My Bushmaster did it back in 1997 when I first built it within the first 100 rounds.  Back then the stronger extractor springs weren't yet available so I trimmed about 2 coils of the ejector spring off and it worked well.

When I took the rifle apart . . . there were a two little pieces of brass on the bolt head that I brushed out when I cleaned it. They were tiny though. . . could barely see them.  I will look again more closely.

Quoted: The other issue may be that you've got some brass shavings in your bolt head that are jamming up the ejector and/or extractor.  New bolts sometimes have sharp edges that weren't properly deburred and will shave off little pieces of brass, until those edges round over from wear. -Troy

Quoted: Can you explain your use of the word extractor & ejector . . . I am not sure I understand what you are saying . . . well most of it I get . . . Just not the difference between the extractor & ejector spring, because you say that your extractor spring broke but you trimmed the ejector spring? Thanks . . . db Quoted: It's because it actually broke in the extractor spring that fast.  May sound impossible but it's true.  My Bushmaster did it back in 1997 when I first built it within the first 100 rounds.  Back then the stronger extractor springs weren't yet available so I trimmed about 2 coils of the ejector spring off and it worked well.

The ejector is in the face of the bolt, it pushes the brass out of the AR15 by spring pressure after it clears the chamber on rearward movement.

The extractor holds on the the rim of the brass and holds on to it as the bolt travels rearward until ejection.

My extractor spring didn't break it 'broke in' meaning it was weaker than new within 100 rounds.  The stronger extractor springs weren't available on the civilian market then so I trimmed off 2 coils on the ejector spring so it would stop over-powering the extractor and it worked fine.  I've heard that this fix doesn't work well on full-autos but it's fine on semi autos.  Now that strong extractor springs are available I no longer trim the ejector springs to make them a little weaker on carbines.  Now I increase the extractor spring power, and slow down the cyclic rate (by gas tube or heavier buffers) which also makes the extraction easier on a carbine because it allows the pressure within the barrel to drop lower before the bolt starts rearward upon firing.  Most carbines bolts start to open when the pressure within the barrel is still very high, much higher than on a 20" standard length rifle which doesn't exibit extraction problems.