Forgotten Weapons video on the Hensoldt device.

From the FW short article:

This was essentially a calibrated flashlight with an aiming point and pressure switch. It projected a beam of light that was specifically 2m wide at 50m distance, with a black spot in the center which would measure 30cm at 50m. This could be focused and zeroed o the black spot was a functional aiming point, allowing both target identification and engagement.

The HK53 is a shortened HK33, which is the 5.56mm variant of the G3 battle rifle.