Sorry everyone is getting pissed about this, get over it :)
You can do this glitch with any launcher :) and works with no ammo
For PC and PS3 users-
1. Have javelin (or other launcher) in your hands
2. Hold down grenade button (semtex or throwing knife)
3. While still holding grenade, hit your switch weapons button
4. Now your launcher should be back in your hands and you can let go of the grenade button
5. You are ready to explode, you can knife, sprint, and jump, but anything else you do cancels it and the process has to be repeated.
If you need help with this glitch message SETNOM19 on Xbox Live.
He told me about it.
Thanks for watching and please sub :)