This is a pistol I made based on the one carried by Impactor in the "Last Stand of the Wreckers" comic series from IDW. The center barrel and the rear wheel rotate and the peg is to fit standard 5mm hands.
This gun has been successfully tested in WSF Polished. The peg is slightly oversized to allow for material loss during the polishing process. If ordered in an unpolished material, some light sanding will be needed for a proper fit.
This gun is also part of a kit I have in my shop for converting FOC Optimus Prime to Impactor. If you really want a great Impactor figure, do it yourself with my kit!