My two cents worth: your BG fabric and the gun have essentially the same luminosity value and thus with direct lighting, they will both reflect the same tonal value. Secondly, I cannot fathom why you would use F/20 when your overall depth of field is less than 3 inches. Rule of thumb is that if the object of your attention isn't moving, then any shutter speed will work. F/4 would be more than sufficient. ISO 100 is as low as this camera allows so if you stay at ISO 100, f/4 then where can your shutter be? 20, 16, 11, 8, 5.6, 4 = 5 stops of light = 15, 30, 60, 125, 250 - If I am letting in 5 stops more light, then I must gain 5 stops more shutter and this always has wiggle room to go up a stop and decrease the speed by half (5.6/125).
As to composition, I would put tiny blocks behind the gun to raise it off the surface a bit and light only for the gun, letting the brass become more diminutive in brightness and position so the handle doesn't get too blanked out in shadow (though it looks ok in Photoshop) and give it a bit more head room.