Hmm One way the addons could work would be like a buff tool no additional buttons or anything then just switch to the tool before you get on the gun (make it look like a power drill or something so it makes sense that your drilling in the addon, and have that for every addon so there is less work used on models for everything) whack the weapon 4 times and voila. I know I know that still requires a new UI and mechanics but its a thought for how it can be implemented without gumming up the UI while the gunners sitting on his gun, or adding in more buttons to be pushing.
As for crazy ammo types here is some more i thought of
Dropper ammo: adds a drop of like 15 m/s to all projectiles shot, 50% less arming time, +10% more damage ( i thought of this due to the dropping mines discussion but figured a new ammo type could get the job done and may be useful for other weapons due to the damage increase and less arming time)
Rocketry ammo: 20% chance of adding a fire stack on the enemy and +60% projectile speed, however every shot adds a fire stack on the weapon your using (I was thinking of having the chem spray stop the fire stacks but since this is a range ammo type its be to easy to keep the weapon chemed and then you would just have a super powerful lesmok. So have the fire stacks added from this ignore chem spray immunity and that may also have the extinguisher become more useful as a niche tool.)
Flat ammo: reduce accuracy, projectiles travel -15% slower, +20% damage increase
shredder ammo: -30% clip reduction, +20% faster fire rate, +20% damage increase, every round deals 10 damage to the weapon.
( Im just pulling these numbers out of thin air and not putting thought into the actual math its more the ideas and the roles that id like to see in the new ammo types)
