Got two things going on, and the big one is the ejection cycle on the rig is on the short stroking side, Maybe.

So the first question is will the bolt lock back on the last shot fired, and by this, is the catch catching the front of the bolt face to hold it back, or is the mag catch only catching the bottom of the carrier to hold it back isntead.

If bottom of the carrier, or not all allow, then start checking for a gas leak, binding, or at problem with the load being either too weak, or too hot isntead.

If the bolt catch will lock back on the catch, with the catch in front of the bolt, then problem is the extractor is not hanging onto the spent case rim on the pull of the case, and the spent case on the bolt face to the back of stroke.
Now lets touch on the scrap marks on the case of the rim.

If you have cycle out a live case, then as soon as the bullet clears the chamber, the ejector is going to cam the bullet to the right in the barrel extension void, and it normal to have the scraps marks on the bullet as you hand cycle out the live round from the right hand lug. To lessen this, you just take some sandpaper and edge the sharp lip of the that lugs edge.

I bring this up, since as the bolt cycles when self loading, the bolt should be coming back with enough speed, and the residual  bore pressure blowing back on the case, that the bolt should be pretty much glued straight to the bolt face until the back of stroke, and will clear the barrel extension lugs isntead.

So if the bolt does not lock back via the catch in front of the bolt, then take a good look at the last round fired spent case, and see if the rim of the round is bent or not.  Not bent, no enough gas, and if bent, then too much gas or the chamber is reamer chattered to hell isntead.

Bolt locks back correctly, but spent case is dribbling out, then extractor is not holding onto the spent case and extractor claw and rim releif channel may need to cleaned up, or may just need to add tension to the extractor spring (#60 O ring around the extractor spring, or swap the standard tension extractor spring to a Colt M4 extra tension extractor spring (colt M-4 extractor spring will be gold and have a black insert in it, as well should have colt on the packaging with the correct labeling as well).

One last thing, don't confuse working pressure of the round, with the amount of pressure a give load is going to send through the gas system.  Hence the slower the powder used to load, the higher it will produce in gas pressure down the barrel gas port.  So you can have two different power burn rates, both producing the same over all working pressure, but the slower burning of the two powders, will produce higher gas port pressure.

With bolt locking back, stroke is fine.
With case rim not bent, it a mater of the extractor dropping the rim on the extraction pull instead.

So make sure your using a chamber brush to scrub the chamber by hand with CLP each cleaning to start with.

Next,cam a spent case off the extractor with the B/C in hand, and make sure that the ejector is not binding in the bolt face channel during compression and release.

From here, pull the extractor off the bolt, and break out a small jeweler file.

Start with the side edges of the rim relief channel under the grabbing claw, and remove any milling burs that may not be allowing the rim to full seat in the channel.  


Next, look at the very side edges of the claw, and if see end of milling burs, remove them as well.  Leave the claw edge sharp, but address and under claw side burs that may be making contact with the rim before the claw edge surface does.


From here,  check the bolt face edge where the extractor seats against the bolt, and clean up any burs there as well.


Lastly, go hit up a home depot type hardware store, go into plumbing, and pick up a few #60 O rings (about a dime each).
Install on of the O rings around the extractor spring to add more tension to the extractor itself.


At this point and the rifle cleaned and upper bearing areas CLP lube correctly, should solve all your extraction problems.

But if with the above, the spent case rims are starting to get bend now, really need to check for over function problems, and/or just a chamber that is reamer chattered ridge and grooved to hell isntead.

In 300 Blk, it not uncommon to have the gas port at  the pistol type location even on a 16" barrel.

This allow the  same gas port size to work with a broader type of ammo;  both weaker type subsonic ammo, as well higher pressure super sonic ammo with the longer amount of bore past the gas port.

Math of bolt unlock timing.

Gas port size, the weight of the buffer and B/C, and the recoil spring tension.
Also included in  this math, it working pressure of the round, and the burn rate of the gun powder that will determine the amount of gas pressure pushed down the gas port.

Hence if all rounds where loaded to the same over all working pressures with different powders, the slowest burning powder would produce the highest gas port pressures, while the fastest burning powder would produces the lowest gas port pressures isntead.  This is due to the max spike dwell (over all working pressure) from the distance of the gas port.

Since we have this graph hand, lets use it.


So bullet is 63gr powder is H335, and loaded to 60K working pressure.
If we use a slower burning powder loaded to 60K working pressure, it will move the spike to the right, and will increase the gas port pressure of the give barrels.

So the rub, bolt unlocking too fast, the spent case is over pressurized welded still to the chamber by residual pressure in the bore for a clean spent case pull from the chamber, and the rig short stroke.  On the other side of the coin, bolt unlock too slow, then ends up short stroking as well.

So if we get away from loads (which can make a great deal difference if a rig is going to cycle correctly or not), then we have recoil spring tension, buffer weight that you can play with to get the bolt to unlock at the correct timing.

In regards to recoil spring, you can go slightly stronger or weaker in tension, but only lightly one way or the other before you cause problem.  Spring too weak, and the action may not lock up correctly.  To much tension, and now the bolt returning will be too fast, and can break bolt catches, as well as cause some nasty bolt bounce as well.

So really, short of mod'g the gas port, this leaves buffer weight, and a lot can be done with such to get the bolt to unlock at the correct timing.  
So with any given ammo, really need to figure out if the bolt is unlock too slow, or too fast, which is really easy to figure out.  Hence police the spent case, and just take a look at the rim of the case, since if the problem is the bolt unlocking too fast (need a heaver buffer), then extractor is going to bend the rim of the spent case from the hard pull out of the chamber.
If bolt is unlocking too slow, then need a lighter buffer isntead.

Math of bolt unlock timing.

Gas port size, the weight of the buffer and B/C, and the recoil spring tension.
Also included in  this math, it working pressure of the round, and the burn rate of the gun powder that will determine the amount of gas pressure pushed down the gas port.

Hence if all rounds where loaded to the same over all working pressures with different powders, the slowest burning powder would produce the highest gas port pressures, while the fastest burning powder would produces the lowest gas port pressures isntead.  This is due to the max spike dwell (over all working pressure) from the distance of the gas port.

Since we have this graph hand, lets use it.


So bullet is 63gr powder is H335, and loaded to 60K working pressure.
If we use a slower burning powder loaded to 60K working pressure, it will move the spike to the right, and will increase the gas port pressure of the give barrels.

So the rub, bolt unlocking too fast, the spent case is over pressurized welded still to the chamber by residual pressure in the bore for a clean spent case pull from the chamber, and the rig short stroke.  On the other side of the coin, bolt unlock too slow, then ends up short stroking as well.

So if we get away from loads (which can make a great deal difference if a rig is going to cycle correctly or not), then we have recoil spring tension, buffer weight that you can play with to get the bolt to unlock at the correct timing.

In regards to recoil spring, you can go slightly stronger or weaker in tension, but only lightly one way or the other before you cause problem.  Spring too weak, and the action may not lock up correctly.  To much tension, and now the bolt returning will be too fast, and can break bolt catches, as well as cause some nasty bolt bounce as well.

So really, short of mod'g the gas port, this leaves buffer weight, and a lot can be done with such to get the bolt to unlock at the correct timing.  
So with any given ammo, really need to figure out if the bolt is unlock too slow, or too fast, which is really easy to figure out.  Hence police the spent case, and just take a look at the rim of the case, since if the problem is the bolt unlocking too fast (need a heaver buffer), then extractor is going to bend the rim of the spent case from the hard pull out of the chamber.
If bolt is unlocking too slow, then need a lighter buffer isntead.