What values in an .ini change how much recoil your gun has? I would consult the wiki had it not been down for the moment.

Mass and veolicty of the bullet.
The higher the velocity the more effect the mass will have, the higher the mass the more impulse will be done to your arm joint/enemy actor.

So I edit the mass and velocity of the stuff under AddAmmo = Round, right?

The mass has to be set on the MOPixel(which can be in there, or be copied from an independent definition).

Shwoops nevermind.

Depending on the code structure, it could be anywhere. Just as long as it's under the MOSParticle heading, which can be under the AddAmmo heading, which can be under the magazine heading, which can be under the HDFirearm heading, which can be under a turret or actor's heading, etc.

An excellent way to reduce recoil is to make your bullets an AEmitter. Thus they will propel themselves, and don't need to be pushed hard to hurt a lot. If you still want some recoil, but not a lot, make the firevelocity low, and the bullets an AEmitter.

Make them fire at zero velocity then use a script to give them some.

It's probably easier to fire them with mass altered to your liking and have a Lua script alter that. This way you retain inherited velocity more easily and generally keep it simpler.