I put a Madbull DD lite rail on my gun, it fit fine. The handguard is not standard size so you can't put any standard RIS that fits between the delta ring and the front ring (unless it's a KWA brand...but good luck with that shit), but any free floating rail system should fit.
This is the exact one I put on my G2X
http://www.airsoftparts.ca/store2/in...oducts_id=1260