You could enchant the guns.
What with? Again, as far as I can tell, either I'm not getting my iteratives (giving me a smaller marginal return on my gun-enchanting investment) or I'm running a multi-gun setup (expensive to enchant.) Is there a Rapid Reload analogue for firearms outside of third-party stuff?
Or you could enchant the ammo bag, Endless Bag of +1 Bullets and so on and so forth?
It's a thought. Don't know of any fully standard and generic enchantment that could apply, though- it's all specific magic weapons/items that are, RAW, arrow-only. Raptor Arrows, Hank's Force Bow, Quiver of Anariel, Quiver of Plenty...putting Morphing on the Raptor Arrows could work if it qualified as a melee or thrown weapon. Even Arcane Archer is explicitly arrow-only.