My suggestion is to start with a thorough cleaning, which includes making sure you clean the chamber with a chamber brush and solvent, then swab it out with something like denatured alcohol, as this will help eliminate any issues with preserving oils, and you will also have a clean and dry chamber to ensure that it isn't a friction issue with casings in the chamber. While cleaning, check to ensure that the gas rings have a seal, the gas key is tight and properly staked, and if the rifle has a gas block that is screwed down or clamped then check to make sure it hasn't come loose or out of alignment. You can also do a stripped bolt carrier test (No bolt, cam pin or firing pin, and simply insert the bolt carrier into the upper receiver about 1" while holding the barrel horizontal to the earth, then slowly start tipping the muzzle downward, and when you get to about a 45-degree downward angle or more with the muzzle, the bolt carrier should slide forward with no friction as gravity pulls it downward towards the earth, if it doesn't slide freely then there may be issues with the gas tube alignment, gas key alignment, machining tolerances, etc, but I wouldn't worry about that as of yet.
Then lubricate the bolt carrier, and make sure you soak the bolt lugs so they are dripping, in Armorer courses we teach to give each bolt lug a full drop minimum, if not 2 drops, this ensures it isn't a friction issue that can occur when the unlocking from battery cycle happens. Use a quality gun lubricant, my preference is Slip2000 EWL (Extreme Weapons Lube).
Then try feeding the rifle with a couple of different types of quality American made ammunition from a reputable ammo manufacturer like Federal, Speer, Black Hills, Winchester, Remington, Hornady. Also try some 5.56 versus .223, as the 5.56 will be hotter, and see what results you get.
As for the buffer, I would suggest leaving it alone at the moment and see what happens at the range with the cleaning, lube, and trying different ammo. A heavy buffer isn't incorrect on this configuration. I wouldn't go heavier, as that would make it worse. You would need to go to a standard carbine buffer if you need to go lighter.
If all else fails to work, then don't modify anything, my suggestion at that point would be to get it back into Daniel Defense's hands as they make a great product and have great customer service.
CY6
Greg Sullivan "Sully"
SLR15 Rifles
TheDefensiveEdge.com
(763) 712-0123
