Tokyomarui m4
 

What kind of metal hopup i can use on my KWA m4 ? I'm not sure metal hopup exist for this gun.

Your post header states a TM, but your thread post states a KWA. No biggie, as they us the same two piece plastic hop up types, and they are compatible with minimal modding.
As for installing a metal one piece, you'd have to cut and mod the front of the lower receiver to accommodate the hop up unit......which can be a little tricky.

Hope this helps.
SHA DO

don't change it though. going to a one piece hopup would be a downgrade.

Oh yes!!! Thx manchovie