Guren is made of precise carbon steel & process  the HV500 Coat for the surface.
This plating reinforced a hardness of the surface so achieve around HV500.
It’s better than stainless steel (from HV200 to 400)
It’ll be kept clean & beauty surface for long time.
Of course, it’s good for anti rust.

Guren 1 is simple design.
The muzzle end has crown cut.
Low cost barrel series but its potential is enough for upgrading.

da Vinci GUREN 1 6.03mm Carbon Steel Inner Barrel for Marui M&P9L GBB (107.4mm)
Metal Construction
High grade precision barrel at 6.03mm diameter for extra power and precision shooting
Suitable For Tokyo Marui M&P9L Series GBB Gas Blow Back Pistol Airsoft Guns
For custom upgrade user, you can choose a longer barrel
Dia.: 6.03mm
Outer Dia.: 8.55mm