The original Rem part is cast metal, then painted.
Honestly, any of the aftermarket options, even aluminium versions are more desirable than the OEM part.
Cheers.
P. S.
All of my builds get PT&G bottom metal, whether a stainless or blued action. They are some of the nicest finished bottom metals out there. I buy them unfinished and they range from $125-199USD. Well worth the money for real steel.