Looking for a scope for an SW MP15-22 that also has rails so that an accessory can be mounted later. My needs are for low power -- either 4x fixed or something in the 3-9x variable range. Use will be primarily at the range @ 25, 50 & 100 yards; occasionally up to 200. Want an illumindated reticle; preferably switchable between red & green with a bullet drop indicator. Would like to keep the $ below 400 if possible.