I do have mods available but I'm thinking now that I can only add certain mods to certain guns....I guess? The problem I have with this is that while googling this question I found that at least one person, in that person's screenshot, had the option to mod the M251S, but I don't. I'm going to try to find and buy the same mod from the screenshot and see if I can add that one or not. Specifically, I'm trying to add the Countermass mod to the M251S.