For the sake of this post I'll be using Delve weapons as a base, for the higher base damage.
Surefire Arquebus
DMG:96 Delay:600 Ranged Accuracy+18 Ranged Attack+10 Enmity-4
Adaman Bullet
DMG:127 Delay:240
Total Damage: 223
New bullet:
Achiyalabopa Bullet
DMG:253 Delay:240 Ranged Accuracy+20 Ranged Attack+20
Total Damage: 349
Difference +126
Speleogen Bow
DMG:221 Delay:600 Ranged Accuracy+18 Ranged Attack+15
Mantid Arrow
DMG:63 Delay:90 Ranged Accuracy+5
Total Damage: 284
New Arrow:
Achiyalabopa Arrow
DMG:87 Delay:90 Ranged Accuracy+20 Ranged Attack+20
Total Damage: 308
Difference +24
And for the "Thats not the highest damage bow in the game"
Echidna's Bow
DMG:248 Delay:600 Ranged Accuracy+40 Ranged Attack+30 "Store TP"+4
Mantid Arrow
DMG:63 Delay:90 Ranged Accuracy+5
Total Damage: 311
New Arrow:
Achiyalabopa Arrow
DMG:87 Delay:90 Ranged Accuracy+20 Ranged Attack+20
Total Damage: 335
Same Difference (ammo didn't change)
So even with the best bow available(barring HQ)
the Surefire with the new ammo: Damage 349
Echidna's Bow: Damage 335
Welcome back Gun Rangers!