I'm using metal bushings, Systema Polycarb Piston, Systema Aluminum Piston Head (makes the FAMAS sound nice, but use at your own risk), PDI 140% spring. RoF barely dropped using a regular battery (8.4v 1500mah).
Mountain rails is possible but given that you're mounting them into plastic I'd be extremely careful about how much weight I mount on em. And you definitely want to reinforce the area where they're being mounted or it'll crack/snap in no time.
And unless you have some 10 year old, original production FAMAS, it has an EG560HT motor (high torque). It's probably comparable to the EG700.
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