The VFC scar is one of those platforms that very few techs are proficient with. I've seen too many improper hop up/barrel installations, stripped selector plates... The thing that pains me the most is seeing how many people drill holes through their stocks to install a shitty gate MOSFET...
In my experience guarder rubbers are tight in the vfc scar hop up. After running different brands of rubbers I've reverted back to the stock one on mine. It fits the best.
Guardians of Asgaard - KF32
VFC H&K 416C
VFC KAC SR16 JL Billet SBR
TM FN Five-seveN