Completing level 5 for the shotgun challenge "Open wide" unlocks a hidden challenge "shotgun sniper" but it is retrospective. There is also a hidden challenge with the rocket launcher, can't remember the name of it but is tied to splish splash.
After those two there are no other hidden ones. Additionally, any kills you've gotten that would go for the challenges that are locked for you will be added once you unlock them. Saves you the trouble and is a good way to avoid having to deal with them.
If you get both of those done and you still don't have the trophy, then give your challenge list a look and see if you maybe skipped something by mistake. If not, then you need to level something else up once more to get it. Anything will do. --- "If I was a dev, I would be proud to point out in a game I made that the best weapon to kill a hoard of children was the flamethrower." - Gigabomber
Lol. Again, YOU DO NOT NEED LEVEL 5 NO SCOPE IN SNIPER TO UNLOCK SURPRISE. --- PSN: http://www.yourgamercards.net/profile/Grimmjow44 Currently Playing: Borderlands 2, Dead or Alive 5. I like grinding for hours and hours