Maybe try playing around with a spawn point to see if you can find the location relative to the idle position where the hand would actually release the grenade. So say, idle position is (0,0,0) and the hand release point is (25,15,150) relative to the idle position…just as an example, try and find the location by trial and error of where spawning a grenade would appear to come from the hand at the release point. Then you could determine the amount of time it takes for the hand to reach that point once the player has decided to throw the grenade. Spawn in a new grenade at that location after a delay of “X” amount of seconds, and destroy the idle one. Then once we get that figured out we can begin to figure out how to get the grenade to travel from the release spawn point to the idle position target.