Here's a hand from the minifig model, only in .ms3d format, so its Milkshape 3D compatible only, use it as a reference model, if your weapon is too big or too small, use the hand to see and delete it when your done, if the handle of the weapon/item fits in between the hand, then it'll fit in the game
Minifigure Reference Hand.ms3dPut it anywhere and open up MS3D, go to File and hit Open and go to the .ms3d file
Enjoy, and it should help