Among the accessory options for the Heckler & Koch MR556A1 is the selection of virtually any optical sight system. While some of these options can be mounted on top of the upper receiver, the rear open sight will interfere with many scopes. To provide necessary eye relief for such optics, the Heckler & Koch diopter rear sight will have to be removed. All this requires is a Phillips screwdriver.
I mounted several long-eye-relief sight systems on the MR556A1, such as those from Aimpoint and EOtech, as well as other optics that required the removal of the diopter rear sight. One example was the brand-new Titanium 4x32 mm Combat Optic from Browe Inc. Called the Browe Combat Optic (BCO), this scope has a lot to offer.
Featuring an average battery life of 2,000 hours (720 on maximum brightness), the BCO can be activated by depressing a waterproof on/off button. With a red chevron, the BCO's reticle has ballistic correction from 100 to 800 meters for 5.56 NATO ammunition and three night-vision-device and 10 daylight settings. The 5.2-inch BCO weighs 17.2 ounces with its battery and has 1.46 inches of eye relief. The BCO's Target Light Sensor automatically adjusts the reticle illumination for ambient daylight brightness. It also an internal BCO Microcontroller, the brain of the unit, which can be reflashed with alternate programs via a sealed port. This port also accepts a remote pressure switch.
The hull of the BCO contains two mounting bosses for additional accessories, such as a CQB sight. Both objective and ocular ends are machined to accept a variety of filters and covers. The BCO comes with an adjustable A.R.M.S. MK II Throw-Lever Mount.