Another tip:
Replay the Campaign mission on Airbase. Sprint through the hangar (or main warehouse facility in the centre of the map) or go down one of the sides and enter through a hatch (window) onto the upper platforms inside the hangar. At the end of each side at the beginning of the match, there are two AI Titans which are preoccupied engaging the enemy teams AI Titans. Use this opportunity to get behind them and score several Critial Hits on Titans.
Community AdminAirbase is generally great for Charge Rifle abuse, even discounting the AI titans.
