The Leapers Accushot series 6x40 tactical reticle intensified scope is excellent for AR-15/M4 carry handle mount, and also includes mount adapter for flat top rail system.  The reticle (crosshairs) can me illuminated red or green as well, providing excellent night and daylight visibility.  Illumination intensity is also adjustable!  Check out these additional features:

• MIM (Metal Injection Molded) Technology Objective-to-Ocular Entirely One Piece Tube with Integral Carry Handle Mounting Deck
• New Gen Upgrade of the Immensely Popular T168, Built On TS Platform to Deliver Maximum Consistency, Recoil Resistance and Most Satisfying Performance
• Molded Integral Precision Windage/Elevation Adjustment Housing – Adjustment Range > 50 MOA in Each Direction
• Tactical Range Estimating (TRE) Reticle Intensified with RGB Illumination for Use Under the Most Diverse Weather/Light Conditions
• See-thru Carry Handle Mounting Deck with 3 Mounting Positions for Eye Relief Adjustment, and Optimal Height to Accommodate Use of Rear Sight
• Ergonomic Eye Piece/Diopter for Precision Adjustment with Excellent Clarity
• 2 Superior Quality Flat Top Adaptors to Use on Picatinny/Weaver or Airgun/.22 Rails, Complete with Retention Thumb Nuts
• Includes Flip-open Lens Caps

Additional speicifications are as follows:

Model: Magnification: Objective Dia.: Field of View: Eye Relief: Exit Pupil: Click Value@100 yards: Length: Weight: Parallax Setting: Batteries:

SCP-T169 6X 40mm 21.3' @ 100yards 3.0" 4.5mm 1/4” 8.7" 22.9 oz 100 Yds CR1620 3V