M310 smooth-bore high-velocity cannon
From Halopedia, the Halo wiki
The M310 smooth-bore high-velocity cannon is a weapon system that is dual-mounted in the turret of the UNSC's M850 "Grizzly" Main Battle Tank. The cannons are jokingly referred to as the "main funs" by the crews of the Grizzly.
The M310 guns are considered to be exceptionally powerful and are capable of utilising canister shell ammunition which produces a large carpet of explosive submunitions, greatly increasing the weapon's lethality against tightly packed targets. The cannons are capable of overwhelming an energy shielded enemy vehicle's defences and piercing its hull in a single volley. When paired, the two cannons have a high rate of fire due to the Grizzly's turret featuring an innovative mechanism that uses the recoil impulse of one gun to more rapidly load the other.
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