Personally I think mute 3s are a pretty hard trick unless you're throwing the trick off of a pretty decent sized jump. So make sure that's not your problem. If you're still having trouble wait until about 180ish maybe a bit less to go for the grab, be sure to pull your feet up to your hands instead of your hands to your feet.
"I don't know what day it is, cuz i just took the biggest poop of my life, so I'm a little disoriented." ~Ian Compton