If you already bought the Devastation Map Pack alone, you don't need the Season Pass for you to have the ripper gun since it is included with the devastation map pack. Just sharing.
I'm glad you were able to use ripper gun.
See you in the game!
Are you playing online? If yes, you should be able to use the gun though.
If you are playing on local, I think that won't work since the gun is an exclusive multiplayer gun.
You can try to redownload the map pack and see if that would work!
Best of luck.
Try what EmeLita said. If you're playing on Local, check from online for the Ripper. You'll need to connect online first before the guns show up from the DLC map packs.