Need assistance on gun modifications

I’m really struggling to understand how the gun mods actually affect the guns they are attached to. I was under the impression that less is usually more since increased volume and mass means longer aim times. For example, would it be better to use an unmodified SMG for clearing the inside a building as opposed to a rifle with a scope, lasersight and adjustable stock?

Yes and no. Some mods don’t affect volume or weight (ergonomic grip springs to mind, if that’s still a thing) and lowering dispersion is almost always a good thing, but fully modded guns can gain quite a bit of aiming time.

It basically comes down to what you want to do with it. Mods are essential to reach high accuracy and handling modifiers make a big difference to automatic fire, but for general usage a quicker gun is probably not a bad idea. Best to experiment, really.

Well I’ve tested the stuff I can craft, and I can’t tell that big of a difference outside of the scope, recoil stock, and foregrip attachments. Where could I find them in the files to see the exact values?

There are a couple of files but they should all be in Cataclysm-DDA\data\json\items\gunmod (one file per attachment location)