(Don't want to push, or sidetrack, but i suddenly really like the impact idea and this thread begs for discussion on it - last post unless people ask for more)
I ran some numbers and based everything off of the power of a single mine. If you have any concerns, run your ship into a single mine and see what that does to you, then consider proportions.
Damage modifier: 0.2
Clip size: 0.7
Gun deals only primary damage, losing the ability to inflict any secondary damage it has.
Primary damage is converted to impact damage.
Per clip, light carronade easily wins, dealing 68% of a single mine's damage per clip. Gatling deals 56%, Hwacha 47%, and Heavy Carronade 45%. All others are below 40% per clip.
Only 4 weapons deal less than 20% damage per clip: banshee (12%), mercury (10%), harpoon, and flare gun (1% lol).
Per shot (for immediate knock-back effects), Heavy carronade loads up 45%, making it easily the best pusher. Heavy flak falls in at 20% (along with mines) per shot before carronade shows back up, along with merc and artemis.
With modifiers in consideration, The most possible damage to deal is 185 to balloon, 154 to hull, 62 to component, or 82 to armor per clip of the light carronade.
I don't know how AOE would come into play (if at all) for how impact damage works when hitting multiple components.
I ran numbers for allowing in secondary damage only and the lumberjack runs away with the show, dealing 160% damage per clip. The next closest was hwacha at 84%, meaning dropping primary damage and applying only secondary damage makes the ammo OP on one gun to the point of non-viability.
I don't have numbers comparing reload times or buffs, and it's on excel, not a google doc i can share, but if it has real interest I can make one. ^.^
The ammo type turns any gun into a utility weapon, and works best on close range weapons (preventing snipers from spamming knock-back). With the heavy nerf of the damage modifier, the guns don't deal massive damage by any means. The guns become effective against armor, hull, and balloon, but can't do enough damage per clip to be truly dangerous in terms of damage (can be nearly effortlessly denied by an engineer making a simple repair. This is not an ammo type your engineer would take - it is next to useless as a singular ammo type. However, a gunner being able to load it in when the opportunity arises, or when their own weapon is not in effective range, or when their weapon can't fire effectively (inside arming times, or firing a gatling down at a ship trying to balloon-block the shots) suddenly becomes much more desirable. A single mine can be devastating when it explodes, knocking off arcs, throwing ships into and out of situations of danger or advantage, etc. The ability to apply that pressure at any time would be incredibly tempting to any pilot, meaning gunners with their multiple ammo types are very tempting.
Thanks for your patience.