This is a L3 SU-231A/PEQ, or also known as the EXPS 3-0. This is a holographic weapon sight that has been issued to all branches in the United States military. This HWS has been used on various weapon systems across the military and has been proven with decades of use. The SU-231A strives in close quarters engagement and passive aiming with night vision devices. This HWS can be found on HK416s, MK18s, M4A1s, M249s, MP7A1s, MP5s, and many other US service weapons. You do not want to be caught in the "donut of death" reticle. Here are some more specifications below.
Weight: 11.2oz (317.5g)
Water Resistant up to: 33ft (10m)
Mount: 1" Weaver or MIL-STD-1913 Rail
Windage & Elevation Adjustment: 0.5 MOA Per Click
Brightness: 20 Daylight Settings , 10 Additional Setting for NVG Devices
Power Source: x1 CR123
Battery Life: 1,000 Continuous Hours at nominal setting 12 at room temperature
Operating Temperature: -40°F to 140°F (-40°C to 60°C)
Country of Origin: Made in USA
*This model is not NAV-SEA marked like some units are.