A cartridge picker assembly may include a frame having a first side wall and a second side wall positioned in spaced-apart relation and a cartridge access end. A lateral guide surface being substantially parallel to a lateral plane is associated with the first side wall of the frame. A thumb assembly is slidably mounted to the first and second side walls of the frame so that the thumb assembly is capable of moving toward and away from the cartridge access end of the frame. A guide member flaunted to the thumb assembly engages the lateral guide surface on the first side wall of the frame so that lateral motion of the thumb assembly is controlled as the thumb assembly moves toward and away from the cartridge access end of the frame.