JG Replacement Cylinder & Cylinder Head Set for M4 Airsoft AEG

"I got this with my JG gun, and i have to say the Cylinder is pretty good. it has a good air seal. I have used the in my G&G GR15, and now I'm using this in my Echo 1 m249 (stock cylinder is crap). I have had this for over three years now and its pretty good piece, probably not the best but its does what i need it to do.