Bolt in hand, cam a spent case off the extractor to compress the ejector in/out of the bolt face a few times to make sure that the ejector is not binding in its travel in the the bolt face channel from all the way in, to all the way back out.

Next pull the extractor off the bolt, install a #60 O ring (about a dime at any hardware store) around the extractor spring, and reinstall the extractor.


With every thing back together, pull the charging handle all the way back, and confirm that the face of the bolt does not retract back past the last of ejector port edge.  The face of the bolt should stop about 1/8" to 3/8" in front of the back of ejection port.

Lastly, use Sweets copper solvent to clean the barrel bore, then BreakfreeCLP (spray can works the best) to clean everything else on the rifle, including the chamber with a bore bush by hand. Also, don't forget to pull the buffer and spring, and give them a C:P cleaning as well.
Note, bore first with sweets, then chamber with chamber brush by hand with CLP, the shove clean patches through the chamber/bore until they come out clean/dry.  After you clean the barrel, then attack the rest of rifle.  As for the B/C parts, allow the CLP to soak on the parts while you are cleaning the barrel and the fouling will wipe of the parts when you get to them.

Once you have the rifle cleaned, then spray a coat of CLP on both the inside and outside of the B/C, give the B/C  quick single shake, insert the B/C into the upper that wet, then cycle the action a few times to migrate the CLP through out the upper bearing surfaces (the gun is now ready to fire with the upper bearing area correctly lubed).

Good catch, no need for the O ring with the extra tension extractor spring installed, so comes down to either bolt face retracting back past the ejection port, dancing the cases back int the action off the back of the ejection port window, the ejector not kicking the spent cases off the bolt face on the back of stroke stall, or short stroking going on with the back of B/C stall not great enough in regards to dead blow effect for a clean pivot point/dwell time of the spent case off the bolt face at the end of rearward stroke.

As for if it is a stoking problem, that would rear its head by not locking the bolt back on the catch after the last round fired out of the mag.

So if stroking correctly, then ejector binding up in the bolt channel or weak spring if you find that the face of the bolt is stopping before the back of ejection port window.

Pick your poison,

Permanent correction is to shorten the end of the receiver extension to be able to thread it in farther to both, index the tube needed for the stock, so the end of the tube retains the buffer retaining pin, and to bring the back of tube end void closer to the receiver to correct the bolt face retracting back past the back of port window.

Or as a quick/temp fix, just pull the buffer and recoil spring, then using fender or large nylon washers down the inside of the tube just a hair smaller in diameter than the tube's ID , shim the tube end of void surface forward that way instead.




Also, as Circuits pointed out, check the buffer bumper.  You did not give a round count, but the bumper had to go way south/shorten out before the back of the key should even be close to touching the back of the lower receive threaded section with the correct buffer in play.

Photo of the buffer bumper please, since if the tube was installed correctly/was in spec, the bumper has to be all peen'd to hell to allow the key to crash into the back of the lower receiver tube threads.

Sully also is a Mod in this Forum, I sent him a IM with a link to this thread

As long as the shims are being held to the back of the tube via the spring, your golden, so don't worry about the light spring tension increase.


But on the same note, when you get a chance, really a good idea to finalize by shorting the tube the needed amount instead.

I always through of your rifle as a personal build, but if the lower can factory with receiver extension, then best to just send it back and have the manufacturer replace/correct the receiver extension.

Also to point out, if you are just running 55/62 grain ammo, the heaver buffer you have in the rifle now is over kill.

Dynapar,
    was the rifle purchased from us or from who?  Any idea of the exact age of the rifle, about how many rounds fired through it total, maintenance schedule and procedure (chamber brush etc), are the gas rings sealing, are you lubricating where all metal rubs metal on the bolt carrier assembly and with what lubricant?

CY6
Greg Sullivan "Sully"
SLR15 Rifles
TheDefensiveEdge.com
(763) 712-0123

Casting??????

Looks like a forged receiver to me (would need to see the non ejector side at the selector to be sure), so best guess, forging instead.


BreakfreeCLP to clean and lube everything on the rifle, except the bore, which Sweets solvent works great since is does not need a lot of scrubbing to remove copper, and does not leave behind a residue that may not get alone with CLP.
And yes, chamber brush by hand with CLP to clean the chamber after you have cleaned the bore,  When done this way, as you go to push clean patches from the chamber out the muzzle, the CLP remnants even after the patches come out dry lightly coat the bore for short time storage.

Does your bolt carrier, bolt, and barrel have any markings on them, if so what are they?  You have a forged receiver (T6 7075).  You are also showing two different pics on the upper, as one has a carry handle and the other has a LMT stand alone rear sight, are these of the same upper?
   
Field strip the bolt carrier assembly.  Remove the extractor assembly from the bolt and inspect for debris, if it has brass shavings or debris under it then scrub with a good solvent and tooth brush and remove any debris. It should have a captured spring on the back side, and possibly an O-ring or D-ring around it. If it has an O-ring or D-ring around it, remove it and clean the spring area. Inspect for an extractor spring insert inside of the spring (blue, black, or possibly some other color), it should have one and if not then get one and put it in. Inspect the face of the spring, it should be wound tight and flat on the top face. Clean the extractor channel where it grabs the lip of the brass casing. Scrub the bolt channel where the extractor goes into the bolt, and while you have the extractor off you can scrub the firing pin track (I like pipe cleaners for this). Lubricate and reassemble the extractor spring assembly onto the bolt.

The ejector plunger should be sitting just below flush with the face of the bolt lugs. Push the ejector plunger backwards into the bolt, it should go below flush with the bolt face (the bolt face is where the firing pin comes out of), you are compressing a spring so there should be resistance, then release the pressure off of the ejector plunger and it should return back forward under its spring pressure. Lubricate the ejector spring (there is a small hole back by the cam pin hole in the bolt where the the ejector spring rides in its channel), and around the ejector plunger on the face of the bolt, then push and release the ejector plunger several times to work the lubrication into them.  If the ejector plunger does not move freely with spring resistance) in both directions, then it needs to be removed and inspected for debris that is causing binding or a possibly damaged spring or plunger.  

Clean the tail of the bolt and inside of the bolt carrier where the bolt goes to remove any carbon build up (Slip2000 Carbon Cutter/Killer) works great for this.  Heavy carbon build up on the back of the bolt or inside the bolt carrier can cause many issues of which one will be a timing issue. Check the bolt carrier gas key to make sure it is tight by trying to wiggle it, and are the gas key screws staked properly (photo please if you are not sure if they are done properly or not).  Once everything is clean, the lubricate with everything with a good lubricant (my preference is Slip2000 Extreme Weapons Lube "EWL") and reassemble.  Once the bolt carrier assembly is reassembled and lubricated, check the gas rings to see if they are creating a seal with the bolt carrier, if they are not getting a seal then I would recommend replacing them.  Then with a clean rifle and gas rings that are getting a seal, go shoot the rifle and see what happens.

Other possibilities are that your buffer spring needs replacement (they do wear out).  Generally when we build a carbine length gas system rifle, we use a heavy duty chrome silicon cryo'd buffer spring and a heavier bolt carrier and heavy buffer (your pics of your buffer show that it is a standard carbine buffer, which means that your rifle may be cycling too fast).  Your gas tube has a bell on it that creates a seal inside the gas key, if this bell is worn off then it could cause malfunctions, we check these with a gauge, and if it worn prematurely then it is usually due to an improperly indexed barrel.  Another possibility is barrel erosion, which can be caused by heated rapid firing shooting session (mag dumps), a diet of tracers, maintenance, or a large amount of shooting.  Inspection for barrel erosion something that we can take a look at if it doesn't turn out to be something simple.    

Greg Sullivan "Sully"e
SLR15 Rifles
TheDefensiveEdge.com
(763) 712-0123

With replacing the front hand guards to a float tube, verify that the center of the feed ramps is centered on the front take down lube,hence that barrel did not slip in the upper receiver barrel socket when the barrel nut was tightened.

On the new gas tube, remove the bolt for the carrier, and using the carrier alone in the upper receiver, confirm that the tube is correctly indexed with the carrier key (will occur  as the carrier gets about 1" from touching the face of the barrel extension. If needed, tweak the gas tube over the barrel to adjust the tube to key).  

Also, if you correctly index the barrel nut top  gas tube channel with the upper receiver gas tube channel, the key will have some flex/movement to it in the upper receiver channel area.  If you find that gas tube very stiff/satationay in the upper receiver, then the barrel nut was not correctly index for the gas tube, and now you have the tube wedged to one side of the upper receiver gas tube channel (not good since you need the tube to be able to wiggle a bit to self correct for the light slop of the carrier fit to upper receiver.

Only problem with that would be that the back of the carrier would not be back to the back of the receiver, and his buffer retainer would have sheared off a long time ago.

Problem still seem like the receiver extension was not installed (shorted when needed to get the bolt to stop correctly against the ejection port) when it was installed.

Number one is buffer retainer marks, with 2 and 3 being rough edges on the back of the carrier.

His light edge scraps on the ST buffer came from him removing and installing the buffer in the receiver extension alone.

Since you have a parts gun that someone built, you could have non-factory parts or who knows how it is put together.  The buffer tube (receiver extension/stock tube) on a Sully Stock is a short fixed tube that is made to a carbine tube length.  If it is one of our factory tubes it will have a shoulder on it that should keep you from under or over screwing it into the lower receiver, as you tighten the tube into the lower receiver until the shoulder bottoms out against it.  Then when you install the Sully Stock it slides over the tube, and the front of the stock will butt up against the back of the shoulder on the tube and lower receiver, and then the stock is held onto the tube with an 1" A2 butt stock screw.  

If the gun is short stroking, I generally look at the four gas seals, and in this case I would look at the the gas tube seal (bell).  Can you post pics of the end of the old gas tube that goes into the bolt carrier gas key, this is an area that has a flared out circular ring that runs about 1/8" back from the open end.
 
Greg Sullivan "Sully"
SLR15 Rifles
TheDefensiveEdge.com
(763) 712-0123