I haven't posted any guns pics, hell I havent posted anythign.. But am a hobbyist photographer.. A few tips off the cuff
I would use indirect lighting as much as possible, supplemented with bouncing your flash off a wall or ceiling. Using a tripod is a must, then go into "M" mode - set your ISO to 400, aperture to F8 or F11, and shutter to 1/45. Go to macro mode if your camera supports it, and if you are zoomed in alot with your lens, pay particular attention to your focus point as your depth of field may be limiteed. Use the self timer feature of your camera so you don't introduce shake when you pull the trigger.. I mean push the button.
;-)