A loading system for a paintball gun comprises a paintball reservoir having an outlet at a bottom thereof. An inlet opening is defined in the reservoir, and a door covers the opening when in a closed position, and movable to an open position. A paintball canister has an opening, and a lid covers the opening when in a closed position, and is movable to an open position. The system is configured such that the canister can be engaged with the reservoir with the door and lid in respective open positions such that paintballs in the canister can flow into the reservoir, and the canister can be locked to the reservoir. The system can be configured such that the door and lid open automatically during engagement, and such that the canister ejects when empty.