You dont need to buy a hop up unit. Just a hop up rubber and nub (sometomes called chamber packing or bucking)
R hop takes a lil technical skill. Try this for a simaler result or google prometheus smooth chamber packing and bridge tensioner (u will have to get the packing from japan prolly tho so i suggest try this and you can swap the nub for a bridge that i think stealth sells)
http://www.airsoftparts.ca/store2/in...oducts_id=2466