In the Tutorial when Jack gives you the thirty-eight revolver you can gain max ammunition for it by simply talking to him over and over. Once should give you the weapon, with some ammo. The next time should unequip it, but you are still getting ammo for it. Do it again and you will re-equip it, you can repeat this as much as you want until you have max ammo for the weapon. This is especially useful if you happen to use up all your ammo shooting at the bottles at the end of the hall.