By inserting his Energon Matrix into the cannon, Big Convoy can transform it into the Matrix Buster. Fueled by this link to the supercomputer Vector Sigma, this weapon is so powerful, even a god might pause when faced with it.
Beast Wars Neo anime
Big Convoy used the Matrix Buster to destroy Unicron.
Beast Wars Neo manga
When Big Convoy is busy fighting Magmatron with his hands, the mammoth nose on the Big Cannon puts the trigger and blasts Magmatron for several times, making him badly wounded.
In a battle against the Predacons on the planet Jörmungandr, Big Convoy uses the Big Cannon to blast Guiledart into pieces out of rage because he interrupts the duel between Big Convoy and Dead End by ordering Saberback fire on them. However, Big Cannon is lost in the last moment when Big Convoy tries to save Break. It is suck into the space along with Saberback and several other Predacons.
According to the event in the episode "Battle of the Single Batch" from Beast Wars Neo manga, the Big Cannon seems to be a part of Big Convoy rather just a weapon. It might be like the relationship between Optimus Prime's component: Brain Center, Roller and Combat Deck in some ways.