I've tried every combination of wording here and on Google and can't find anything close to what I'm looking for, with most posts just being about the online. So I apologise if this is Alex and answered but I was too stupid to find it.

So whenever I find a gun on the ground in the campaign, there are orange parts on the picture that pops up. Not that the gun is actually orange. It looks like it's showing me the base gun, but the orange are parts that would be like performance mods. I haven't found 2 guns that are the same but with different "mods" to compare my idea yet, though I have occasionally found the gun I'm carrying and sometimes instead of just picking up ammo, I get there option to switch guns. While you would be a useful test now that I've finally thought of it, it would still be a lot more useful if someone had a comprehensive list of what these things are and what they do on each weapon as it were. Any information would be appreciated though thank you!