You can't seriously have a use for all those weapons you have? Be harsh man, you've gotta get rid of some stuff some time. Remember, there's always a chance of picking up a weapon a second time, so if you don't use something at all but you "like" it, get rid of it and maybe hope you pick it up again. I literally keep my best of each weapon category (ie. hand cannon, auto rifle), and if there's anything that I really like (such as a weapon I used loads, and it all levelled up, but I no longer have a use for), I'll stick it in the vault. I have 6 primary weapons overall.