DD MK18 w/ Law Folder undergassed issues.

Hello all! This is my first post on the forum to I apologize in advance for any formatting errors this may have. After years of waiting I finally got my hands on my dream firearm: The Daniel Defense MK18. I ended up snagging the pistol variant with the law folder during a Black Friday sale. Long story short after going to the range I quickly was able to identify that it was quite under gassed. I was experiencing quite a few failure to extracts regardless of what magazine I used and when I was able to get it to operate somewhat well the bolt always failed to lock back once the magazine was emptied. After reading a few forums on here it seems that I need to swap the buffer out. I suspect this has something to do with the extra length added by the law folder. On the Daniel Defense website the pistol is listed to have an H buffer installed. What buffer should I be swapping to to help mitigate under gassing issues?

Greg "Sully" Sullivan

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.

Greg Sullivan "Sully"
SLR15 Rifles
(763) 712-0123


The law folder adapter is approximately two ounces which when added to a h buffer is approximately the equivalent of an h3 buffer. That being said MK18’s are notoriously over gassed and should have no problem cycling with quality ammo. I would also look for wear marks in the upper receiver and on the BCG once you get it clean. Finish coming off of the bolt carrier on the rails and charging handle is normal.

You’re intro said your a range safety officer. Do any of the guys your work with have an armorers course and maybe some gauging equipment? I doubt the CRANE gas block on a MK18 is loose but quality companies do screw up some times. The LAW folder may not be installed properly causing some sort of binding.

Is there any issue with extracting unfired rounds?