Pull the buffer and recoil spring.

On the recoil spring, check for end of coil wind burs that are either scrapping down the inside of the receiver extension, or down the sides of the buffer.  If burs are found, then use a file to remove the end of coil wind burs to solve that problem.

On the buffer, check the face of the buffer bumper for signs that the butt stock screw is too long (or you have debris in the receiver extension) and the reason that the buffer if binding up on something in the tube instead.


While you have the buffer and recoil spring out, make sure that the receiver extension has been installed to retain the buffer retaining pin in correctly,  Hence the lip of the receiver extension should dam near be kissing the center post of the buffer retaining pin; so it hold the pin down far enough to not bind on the the bottom U slot of the carrier.

Now take a good look at the top of the hammers firing pin contact pad, and the bottom of the carrier.  On the forward stroke, the carrier has to be able to glide back forward on the bottom of the carrier over cocked, and to two are a mess, then it will cause the bind city.

Empty mag in hand and upper shotgunned open, insert it into the well and make sure that the catch is being raised cleanly by the empty follower.   If it is not, then make sure that the bolt catch is not binding up in the receiver slot, and needs to be hand worked with lube to loose it up in the slot.  Also, when you pull the mag, the catch should spring load drop cleanly as well.   One last check on the bolt catch, and that is to take a good look at the upper  back top side edge of it.  Hence when the mag raises the catch, the bolt face slammed into the lower section of it, and if you have major tag marks on the top edge of it , then the height of the bolt catch is too high in the receiver, and the bolt is catching it in the down position isntead.

One more check, and that is to dry fit the carrier with key (bolt removed) in the upper receiver to confirm that the key is not too wide for the upper slot, the gas tube is correctly aligned with the carrier key, and that the key is not binding in the U slot of the charging handle.

Get back to me on the problem area found and I will walk you through the needed corrections to solve the problem.

P.S, the Marine veteran card has no merit here, since we both know that in the service, if you have a problem with your rig, you hand the rifle to the armor; Which is the only person that is allowed to strip the rifle down past the basic cleaning service level to fix it problems.  

Hence, here is your TM to clean and use the rifle
http://www.ar15.com/content/webPDF/TM9-1005-319-10.pdf
Note, if you are an old fuck, then here is the cleaning manual you got to not only maintain the rifle, but something to look at when  to rub one out to late night in the fox hole as well (Trust me, she is hot as fuck when you been in country way too long without getting laid for too long as well).
http://www.ep.tc/problems/25/02.html

While here is the armors TM to fix the rifle instead,
http://www.ar15.com/content/webPDF/TM9-1005-319-23.pdf

If you are focusing on the gas ring, then your looking at the wrong parts.  Hence the bolt is well out of play at the back of the stroke, would not cause a B/C to stick back in the rear position.

To add to the check list, double check the pawn on the forward assist, and make sure that is not protruding into the upper receiver void and catching the side of the carrier when it trying to move forward at back of stroke.

Lastly, I an under the assumption that the B/C is binding up all the way back at the end of the rear stroke, and if this is not the case, and the bolt is binding up at some point of trying to strip a round out of the mag instead, then it does change the things needed to check.   So on that note, post a photo of where the bolt is binding up on the forward stroke, since it will narrow down what needs to be checked.

If the bolt catch is being raised via the recoil (all the way up), and pressing the bolt catch release is sending the bolt home, then there is a problem with the bolt catch spring, or  the spring channel.

So start with removing the bolt catch, via taping the side of the receiver so you don't scratch it with a long punch, and either drive the roll pin out the front of the channel, or in regards to bolt catches that use a pin that is screwed into the receiver, un-thread the threaded pin out the back side.


Now since the bolt catch spring and bolt catch buffer are .154
http://www.ar15.com/content/webPDF/lowerBlueprint.pdf
Section C-C bottom left hand side.
.660" minus .220" =.470" (=/- .004") should be the depth of the channel for it face in side the slot).

Lastly, check the bolt catch spring to make sure it the correct one in play, as well to make sure that the bolt catch spring buffer has been installed (it goes spring first into the channel, then buffer, then catch.



The last check, with the catch back in play, is to check the tension of the bolt catch, and to make sure that although an empty mag follower will be able to raise the catch, its still spring loaded back down to hold the catch down during recoil of the rifle.  

Hence on a rifle that only weights 6.5 lbs, there is not a lot of mass to the rifle to combat the normal felt recoil of the round and buffer off the back of the tube, and this could be half the problem is itself if the bolt is semi over functioning as well.  If needed to get the bolt back into check if an over function problem, a heaver buffer or strong recoil spring can be installed to help slow the bolt unlock speed down.

Regarding the bolt catch tension, again the tension of the catch has to be that a empty mag follower has to be able to raise the catch, so these is only a small window of adjustment that can be made with the tension of the recoil spring isntead.

Simply put, with the felt recoil of the light rifle, this alone may be the reason that an in spec bolt catch's spring tension may not be enough to keep the catch down during recoil isntead.  So if the problem is not a spring tension one, the felt recoil of the rifle seems reasonable to other rifle, then it may boil down to having to lighten the bolt catch to resolve the problem.

On the other hand, if the bolt catch is only be slightly raised, to slightly catch the bolt face during recoil, then it may be that the top surface of the bolt catch is too high, just lowering the top surface of the bolt catch may all that is needed to solve the problem isntead.

So need a photo inside the ejection port with the bolt pulled back to just behind the catch to see the clearance between the two when the catch is at home, the catch raise all the way up to see the amount of engagement once it has been raised all the way up , and then the amount off pressure it takes to push the catch back down with the upper shotgunned open, and a empty mag follower pushing the catch up (should be around 4oz, and not where near that the same amount of pressure it would take to push the mag follower down with the catch in play as well).

Or, just box the rifle up, and send it back to the manufacturer to resolve the problem isntead.  
Hence the 300blk is going to have harder than normal recoil in a light weight gun then say a 223, and they may need to come up with a solution to resolve the bolt catch from bouncing up under it slightly above normal recoil for the light rifle instead.