If you, like me, suck with the sniper rifle and barely used it the whole game, the best place to do this is at the final boss battle, Command Deck, right at the beggining just take the rail to the top part of the ship, and there will be a barrel with a sniper rifle on it, just take it and aim for the enemies down at the deck, they will be focused at the ship's core so you can take your sweet time aiming at them! if you run out of enemies just reload the checkpoint!