M512 Smooth Bore High Velocity Cannon

The 90mm High Velocity Cannon is the primary weapon of the M808B Scorpion MBT. The cannon is 90mm caliber, and is capable of dishing out immense damage from shrapnel over a fair radius, and can penetrate a good deal of armor, like that of the Covenant Wraith Tanks. It fires a tungsten sheathed Armour Piercing Ballistic Capped (a type of round that sacrifices armor penetration for larger amounts high explosive filler) round at high speeds and can cause havoc when used on exposed enemy infantry. It is very effective for destroying light vehicles and enemy emplacements, like a Shade or Lookout tower.

Ammunition
It should be noted that in the Halo Universe, traditional shells have replaced the Armor Piercing Fin Stabilized Discarding Sabot Round used during the later half of the twentieth century. Whether this has to do with advances in ballistic performance, newer explosive materials, or different firing mechanisms is not known.

This type of shell is designed to first penetrate armor, then either by sensor, shock trauma, or via a chemical fuse similar to the Raufoss Mk 211 to detonate the high explosive filler inside the shell to cause further more damage. Traditional Armor Piercing rounds are designed to penetrate armor and are less effective at destroying the inside of the tank, whereas High Explosive shells are made purely for knocking out emplacements such as bunkers and buildings but are useless against armor. This shell combines both of their qualities, but is less capable of doing both duties.

Advantages

 * It can destroy most vehicles with one shot; for the Wraith, it takes two to three shots, depending on the difficulty. Additionally, it can destroy a Phantom in 2-4 shots (only on Halo 3).
 * It can be used for long range assault.
 * Can easily kill Hunters with one shot.
 * The tungsten armor piercing rounds travel at a very fast speed and is difficult to dodge, making it highly effective against more mobile enemy vehicles such as the Ghost and Chopper.

Disadvantages

 * It cannot fire on anything too close to the cannon as the cannon cannot traverse that close.
 * It leaves a smoke trail when fired which would expose its location to any opponent.
 * The area-of-effect means that precision kills are next to impossible - friendly units near the target are likely to feel the force of the blast as much as the target.