Where can I buy the muzzle brake castle nut set screw? I really don't want to have to order one if I can help it. I know it is 6x40 thread but all I can find locally is 6x40 3/16's set screws, and these are not as long as the OE set screw nor do they have the taper that fits into the castle nut gap. Does anyone have the exact size? Thanks!