And if you prestige you have to unlock all the guns again but everything you unlocked for them are still there and all your challenge progress is still there. Plus you get a permanent unlock every prestige level.
If you never prestige the weapon BUT prestige your rank, when you unlock that weapon next time through, all your attachments and camos will still be there. Its a rather quick process, I would suggest to prestige rank AND weapons. The weapons only need prestige
twice and rank needs ten prestiges.