From Halopedia, the Halo wiki
The Projection sight is a holographic sight used on UNSC weaponry. The projection sight doesn't take the form of a physical scope; rather, it holographically projects a targeting sight in front of the weapon to provide more information to the user, such as ammunition count. To ensure accuracy, shapes that line up with the weapon when properly oriented are also projected.
Known applicable weapons
The following weapons have been seen to utilize this attachment:
List of appearances
- Halo 5: Guardians (First appearance)