WE Hop up assembly.
 

My self along with a fellow team mate are doing intnerchangeable uppers for our we m4's so we can changer them to m16 uppers, we have been having a hard time trying to get the hop up unit its self. Would anyone know where we could find them and are they avalible in metal? We upgrading them to C02. If anyone has links or info it would be much appreciated thx.

If you are using an open bolt setup, cheapest and easiest is to buy a conversion kit for open bolts. It includes hop-up unit, barrel and outer barrel.\

For closed bolt, simply get the Falcon upgrade and stock cylinder (lots for sale here since a lot of peaple converted).

I have only seen the m4 conversion kits. I need one for my M16 upper i think it would be a waist getting all the other stuff when theres no need for it. Or do they have an M16 kit?