This script modifies the behavior of the "Max Ammo" power-up to match that of Black Ops 4; it replenishes the ammunition currently in the chamber, meaning it is not always necessary to reload when a "Max Ammo" appears.
Link: https://github.com/NewMartinLag/Bo4-Max-ammo
How to install it: Place the .gsc file in: %localappdata%\Plutonium\storage\t6\scripts\zm.
If you don't have the "scripts" folder, create it; then, inside the "scripts" folder, create a folder named "zm" and place the script there.