What type of stock system (rifle length or carbine length), buffer spring and buffer being used, as you state you upgraded the buffer to one that is 2oz more?  Any chance you could post pics of the feed ramps or damage on the ammunition?  If it's a feeding issue, have you tried to go to a heavier buffer spring to give the feed more push forward, and if so did this give different results?  Also have you tried different magazines, specifically labeling them so you can see if the problem on feeding is with one particular magazine for with all the magazines?  


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

Photo of the when the rig fails to feed,  and where the bolt face is stopping at the jam, tells me a lot about the problem.

If bolt stopping on top of back of case, then either B/C is not coming far enough back to get behind the ammo rear rim*, or mag is not retained high enough in the mag well, or not recover fast enough to get top round tight against the entire bottom of mag lip before the bolt start to move forward again.

* the fact that you changed the buffer mass, and even the gas block, could be the problem at hand.  Here, the simple test to tell if all is correct, load a single round in to the mag, fire the round while leaving the empty mag in the well, and make sure that bolt is locking back on the bolt catch (bolt face in front of the catch). With an adjustable gas block in play, make sure once you have it set, adjust it to allow slightly more gas through the system, as the rifle starts to foul and will need that slight more gas.


As for this being a civilian rifle, really need to check the chamber and leade, to see if tight 308 reamed to promote accuricy with shorter leade for longer ogive bullets, or is looser side wall dimension and slightly longer leade for FMJ ogive bullet to promote reliablilty instead.

Hence tight chamber, with short ogive to give shorter jump to land with longer ogive bullets, is going to end up with 150fmj ammo pretty much embedding into the rifling at loading, which cause a spike in the working pressure of the round as well.
The easy to to see if this is the problem, remove upper off lower, remove B/C, drop a loaded round into the chamber and tap the back of the round with a wooden dowel to make sure case shoulders are tight against chamber shoulders to get with.  Then tilt muzzle up, and live round should free fall out of chamber.


Next, need to know if this is a long action with long stroke, or if short action with long stroke isntead in 308.
The difference, is pull the charging handle all the way back, and tell me the distance that the face of the bolt retracts behind the bolt catch, that the last inch of pull is no greater then the center of pull, and where the bolt face is stopping against the back of the receiver ejection port window.  If bolt face stops in front of back of ejection port window by 1/8"~1/4" and behind bolt catch, the long action, long stroke.

If bolt face stops behind the back of ejection port (to get behind the bolt catch), then short action and long stroke, and need to see a photo of the bolt face.  The reasons behind this, is at end of buffer rear stall, where the spent case is starting to be pivoted off the bolt face and ejection, inside of ejection port back is in the way, and the bolt face has to have twin ejectors, to control the spent case ejection off the bolt until is moving forward in front of the ejection port window and the case be ejected cleanly, and at the same time, the spent case not being let loose to possible knock the top of back of the rim down in the mag, to cause a bolt over problem isntead.

As for bur on feed ramps, may allow for a cleaner feed up the ramps, but in most cases, should not be a problem with the rifle jamming.  Hence if getting bullet tip strikes below the feed ramps, then problem is the mag itself, with either the mag catch not installed with its inner threaded section flush to face of button, or mags themselves not recovering correctly to get the entire live top of round tight against the bottom of feed lip for a clean strip isntead.

As for other jams, could be that hammer top of contact pad is catching the firing pin stop collar to slow the forward stroke down, assist paw catching the side of carrier slots to slow the carrier down on the forward stroke, or something stupid, like O ring on the extractor spring adding so much tension, that extractor can not spring open at last of the way forward, to allow the live round rim to shape into bolt face, so extractor lug can clear the barrel extension lugs to allow the cam over to lock up.

Also, if you screwed around with gas block, the make sure that gas tube is correctly aligned with carrier key as well.  To test, remove bolt from carrier insert carrier with finger in the back to push it until it face touches the barrel extension face, then tilt muzzle upwards to make sure carrier can free fall back.  The gas tube enters the carrier key when front of carrier is about an 1" from touching the barrel extension face, and if not aligned, can cause the B/C last of forward movement as well.  If gas tube needs to be tweaked to align with key, then its tweaked over center of barrel, not the back side that is protruding out into the receiver tweaked isntead.

Bottom line, welcome to the site, and just need more information if the problem is just break in that should self resolve with a bit of live fire and cleanings (including the mags pulled down and CLP cleaned as well), or something that you induced with the parts changes instead (and the ammo its being feed).


Also, going to add, if rifle shoots fine for a mag, then starts to have problems, either something causing a gas leak, or your using the wrong solvents to clean and lube the rifle; with it just fouling choking out too soon.

What specific brand NATO FMJ ?  ( ZQI sucks... )

No offense intended... make sure the chamber and bore is clean of any storage / OEM oil... then relube properly the BCG, and recoil assm.  Plan on giving ample lube for "break-in " ( you might wear some of it upon firing , Lol )

Do the "one mag fed round , fire, bolt locks back 100% test" first.

Adjust the gas block as needed.

Then focus on / look at feeding issues... then look at extraction / ejection issues.

No offense, but baby stepping will narrow down the issues.

Post clear pics of fired cases as need be. We will be looking for rough chamber marks.

Generally speaking, Large Frame AR's tend to need a good amount of lube during break-in.

"L" means light... "G" means Generous.

Thank you for the update. Glad it worked out !