The XBR55 Service Rifle, more commonly known as the XBR55 Battle Rifle, is the first model of the BR55 line; it is described as "a prototype long barreled weapon with an Telescopic Sight." The weapon fires 9.5MMx40 FMJ SAP ammunition from a 60 round magazine  and has a range of at least 900 meters. It was issued to Staff Sergeants Avery Johnson and Nolan Byrne as well as their militia squads' marksmen, Critchley and Jenkins by Lieutenant Commander Jilan al-Cygni for use during the Harvest event during the year 2525.
- This was the first weapon to be used against the Covenant and caused the first alien casualty in the Human-Covenant war.
- The XBR55 resembles the BR55HB SR much more than the standard BR55 model.
- When first used by Avery Johnson, he observed that it had a 60 round magazine. However, the cover shows the ammo count as 36. Johnson may have already fired off a few shots, or this could be an error on the part of the cover artist.
- This weapon has a switch which can alternate the firing mode from three-round burst to single-shot, which apparently did not make it into the final version.
- Halo: Contact Harvest (First appearance)
- M392 Designated Marksman Rifle (Halo: Reach)
- BR55 Service Rifle (Halo 2)
- BR55 Heavy Barrel Service Rifle (Halo 3)
- BR85 Heavy Barrel Service Rifle (Halo 4)
- Type-31 Rifle (Halo: Reach, Covenant equivalent)
- Type-51 Carbine (Halo 2 and beyond, Covenant equivalent)
- M395 Designated Marksman Rifle (Halo 4)
- Z-250 Directed Energy Engagement Weapon (Halo 4)