When you state it was short stroking, do you mean that it was not ejecting the empty casing?  Start with a thorough cleaning of the barrel, chamber, and bolt carrier assembly, making sure you use a chamber brush.  Then lubricate the 7 bolt lugs and rails of the bolt carrier assembly until they are good and wet (glissening like a glazed donut) with a quality lubricant, my recommendation is Slip2000 EWL (Extreme Weapons Lube).  Have you tried different quality American manufactured ammunition?  The PMC is often times found to be softer shooting, so maybe try something else to see what results you get.  Also make sure that your gas block is in proper alignment.  As for the unburnt powder that can be seen in the pic, did you have a misfeed where the bullet was pushed back into the casing?  

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

Check the spent case rims for signs that the extractor is starting to bend the rim on the extraction pull.  This will be caused by over cycling, or the chamber rough or not cleaned correctly.  If the if no signs of a heavy extractor pull, then the problem is not enough gas pressure down the gas port to cycle the rifle correctly instead.  

Now before you touch anything elese, check the gun for leaks in the gas system, or even the gas block not installed correctly on the barrel and it partial blocking the barrel gas port.

Now the fact that the ammo is leaving a lot of unburnt powder behind, would dare to guess that the ammo gun power being used for those rounds are on the slower burning side, and the problem may be a under stroke due to lack of gas port pressure instead (if the gas port in not leaking gas system/ the barrel gas port blocked by the gas block not installed correctly).



As for a 10.5" barrel, it can very ammo sensitive and some ammo's may over function, while others do not have enough pressure at the gas system to cycle the rifle correctly instead.  Short bus, you are shooting ammo with gun powder meant to be burned in 16" of barrel or better, and depending on burn speed of the gun power being used to load the ammo, it's what causes the ammo sensitivty in the very short barrel will little bore past the gas port.

As for cheating, the game here is to add bore back pressure with a muzzle device, which allows more back pressure/acts like you have longer bore after the gas port to allow for a wider gun powder speed burn of ammo's.   The flaming pig is one type device that will add bore back pressure, while a suppressor will as well.


Lastly, leave adjusting the gas port as the last option if you find the rifle under gassed, since buffer mass, and even recoil spring tension are faster to tune a rifle in for select ammo's instead.

And for a quick read since 10.5" cycling problems are nothing new,
http://www.ar15.com/forums/t_6_23/199901_10_5_Upper______and__thing_won_t_run_.html

Over gassed and under gassed cause the same short stroking problems.

In under gassed (pressure through the gas port), not enough carrier pressure through the gas tube to drive the carrier to unlock fast enough so it will full stroke.

When over gassed (pressure through the port again), bolt is trying to unlock too fast with the residual pressure of the bore too high, pressure welding the spent case to the chamber wall, and the force of the bolt trying to pull the spent case looses too much momentum for the B/C to full stroke as well.

To add insult to injury, with what little bore there is on the 10.5" barrel after the gas port, the barrel is very, very ammo sensitive if the rig is going to stroke correctly. It not the over all working pressure of the loads, but how the powder burn rate that can change the pressure at the gas port instead.

So on that note, best to try a few different type ammo's first to weed out ammo problems.



As for checking gas system for leaks/blockages.

CLP sprayed around the gas block to barrel and gas tube to block, then using a rubber hose on the gas tube end, pressurize the gas tube with about 100lbs of air pressure to start checking the block for leaks.  On the B/C, CLP around the base of the carrier key, then hold the bolt in and pressurize the front of the key with around 100lbs of compressed air.

On the gas tube to block, maybe a few light bubbles, but on the block to barrel, and the key to carrier, should have no leaks that these connections.


As for gas block passage to barrel gas port alignment, pull the block and look for the fouling circle caused by the gas block passage around the gas port.  The burn/fouling circle should be centered on the barrel gas port.
Note, gas block set screws are loctite in place.  So to loosen the set screw, old donor Allen wrench in the set screws, heat the allen wrench to glow until you smell a sweet smell of the loctite bond breaking down, then swap to a new Allen wrench to loosen/remove the bolts. Again, swap to a new Allen wrench since the one you just heated up with a torch to transfer heat, you just annealed it, and it's no longer hardened.

Need to see the rims where the extractor was pulling out the spent case from the chamber, but looking at the 5 case from the left, looks to be a problem with over function, and a heaver buffer is needed to slow the unlock back down to allow more residual bore pressure to drop down father at unlock for a cleaner spent case pull.

Also, your running the upper way to dry, so apply more CLP to the inside/outside of the B/C before firing the rig. The CLP will migrate to the rest of the upper receiver bearings areas to keep them better lubed.

Case dings are nature of the beast with the faster cycle speed of the shorter barrel.   Velcro on the deflector will keep the brass from being dinged so hard.


Back  to the spent case rims, not seeing the signs across all the rims of over function for the lot (just maybe on case 4 from the right), and wondering if the problem is a chamber condition or lack of lube for break in problem instead.

Did this barrel start off as a SBR barrel, and refresh me on who this barrel came from.

From your pics, this thing looks bone dry.  Start with a thorough cleaning, then lubricate the 7 bolt lugs and rails of the bolt carrier so they are glissening like a glazed donut with a quality lubricant like Slip2000 "EWL" Extreme Weapons Lube.  Try some different ammunition to make sure it isn't ammo related.

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