M225 Semi-Armor-Piercing High-Explosive
The M225 SAP-HE is the standard issue ammunition for the M6 series of sidearms. Performance-wise, the round is effective against infantry, especially against unarmored or unshielded opponents. Compared to the M118 7.62x51mm and the M634 9.5x40mm rounds, the M225 is a relatively effective round against energy shields due to its high explosive ammunition properties. It is largely ineffective against vehicles, as it is not significantly armor-piercing.
Due to the semi armor piercing nature of the round it is likely coated or made of a hard metal such as steel but deforms shortly after impact to prevent the bullet exiting the body and causing accidental casualties. The filler is likely a stable explosive with either a contact explosive detonation (somewhat counter acting its SAP nature) or a delay action fuse so it goes off shortly after impact, ideally in the body of the enemy, often lethal and crippling.
- The ammo packs for the M6D in Halo: Combat Evolved have a type error: it says 'HP' rather than 'HE'.
- The concept art in Art of Halo 3 refers the M225 SAP-HE as the 12.7x30mm instead of 12.7x40mm. This type error carried on in the Magnum entry of Halo: The Essential Visual Guide.
 List of appearances
- Halo: The Fall of Reach (First appearance)
- Halo: Combat Evolved
- Halo: The Flood
- Halo: First Strike
- Halo 3
- Halo: Evolutions - Essential Tales of the Halo Universe
- Halo: Reach
- Halo 4
- Halo: Spartan Assault