A sabot should work. Depends if he is going for accuracy of the rocket or accuracy of the game. Anyone who doesn't know what a sabot is, it's a sleeve of sorts that hugs the rocket and the inner walls of the tube. Usually used to keep all the force of the propellant behing the round being fired. The usually come in three to four peices and fall away as the projectile leaves the tube. In essence the rocket with a sabot will leave the tube at a perfect trajectory, instead of being cocked to one side.