This steel bolt carrier is made by precision CNC process for M4(T.Marui) GBB/MWS.  Specification of this bolt carrier includes:
Steel body is heavier than the original T.Marui zinc alloy bolt carrier.  Heavier weight provides heavier recoil shock.
Smooth surface and modified body-shape increase smoothness of blow-back action.
Steel material strengthens construction, and it has outstanding durability and reliability in bolt-lock.
An enhanced polymeric wheel ensures smoothness blow-back action and protects the full-auto sear from wear off.