^ Members of Flickr PMG group made lot of custom parts (both recreations, and totaly custom things), and thanks to Import/Export function in PMG you can use them for your creations. I think that some of those parts and codes for them was posted also on this thread.
i tried making believable but futuristic guns
note: its big because it doesn't shoot bullets it would shoot plasma based rounds
a.armor penatration system(uses extra ammo to fire a higher proplled round)
b.grip/rapid fire module(extra cooling allowing for faster bursts)
c.variable noise tracking scope(identifies sound invisible to naked eye showing heart beat footsteps and explosions to apear orange)
a.plasma cutter (generates a fine powerfull plasma blade)
b.mutant scope (has the ability to show both a red dot and a reflex dot