At Rank 1, your Hit with any ranged weapon is increased by Rank*2.
At Rank 4, your aiming ability has been thoroughly developed, especially when it comes to firearms. This allows you to equip Guns regardless of your Main Class. You also reduce the Battle Weight of Guns you equip by Rank.
At Rank 5, you can display your mastery of trick shots and sniping, increasing your Attack Range with ranged weapons by 1.