Special Ammo Boost is useful for similar reasons, as it increases the attack power of your special ammo. Free Elem/Ammo Up increases your HBG’s loading capacity. The increase itself will depend on the size of your original magazine and the type of ammo you’re using — certain ammo types...
Since the LBG is (obviously) a gunner weapon, the MHW best Light Bowgun skills will be ones that boost our ammo strength and capacity. Different skills boost different ammo types, so be sure you’re slotting in the right ones when you put your build together. Artillery, Normal Shots, ...