For Sale $200
This is a brand new, nickle plated kit that sells for $260 currently on sale. Come in new pistol case.
I bought 2 of these kits, one for myself and one for a friend who I was building an AR for. He went with a 20" barrel gas system which this does not fit on. I have used this kind of kit on my own m4 and work great. At least $100 cheaper than any other kits out there and works great in my option. Do your own research first.
I just copied this from the TNW website
New from TNW Firearms, Inc. The GAS piston assembly kit is now available for all barrel lengths with the following barrel diameters (measured 1.5 inches inboard of the site): 0.875, 0.850, or 0.640. This covers most barrels in the 16" barrel range including the M4.
TNW has developed a low-pressure, long-stroke gas piston design. Why a long stroke? In order to keep from "hammering" the bolt as the short stroke designs do. We have slowed down the acceleration of the bolt mass and instead accelerated it over a greater distance. The result is less shock forces on the system, longer lasting parts and reliable feeding. It's the difference between unlocking your bolt with a ball peen hammer or accelerating it on a cushion of air!