Grip Claw boosts the length of moves that deal residual damage at the end of each round and lock the opponent Pokemon in battle (preventing switch).
Outrage doesn't deal residual damage, nor prevents your opponent switching out (YOU are the one locked into the move)
The Grip Claw only affects moves that bind or partially trap the opponent (found here if you're interested); just being a multi-hit move won't cut it, unfortunately.
Source
Hope this helped!
