This trophy can be a bit troublesome at first. The best strategy to get an "A" ranking with each weapon, is to make sure that you hit the dead center of as many targets that pop up as you can. You'll know when you successfully have because a buzzer will go off. Besides the message of the advancement in grade level that appears on the top center of the screen, the best way to know if you're doing good is if you never have to reload the gun during each range segmant. If you don't get an "A" rank in the first 2 segments of the gun range then reload the game and if you don't one in the last, IMMEDIATELY pause the game when the results appear and reload the game.