This page contains a summary of weapons that are used as crafting ingredients in Blueprints. Once a weapon you are not interested in keeping reaches rank 30, instead of selling it, you might want to check if the weapon is required as a crafting ingredient of another weapon: Use CTRL  + F  or ⌘  + F  to use your browser's search function. Crafting another weapon does not mean the product weapon is necessarily better than any of its ingredients.