35mm autocannon

The 35mm Autocannon is a Covenant Loyalist vehicularly-mounted weapon mounted on the Brute Chopper.

It is a semi-automatic 35mm cannon.

The 35mm Autocannon's are the primary offensive asset of Brute Chopper's, and each Brute Chopper is mounted with four linked forward-firing 35mm autocannon's.

It most likely uses a Gast mechanism http://en.wikipedia.org/wiki/Gast_gun.