Whoa.....let's just back up the truck. For those with access to the Carbine Club's Newsletters, have a look at #350, and then #330. Is Frogm1's one of those, a presentation carbine? It would be interesting to find out if his carbine is all STD PRO. The photo in NL350 shows a STD PRO receiver without a S/N. The S/N has not been removed, it never was there. The "S" and the "O" have not been double struck, they are slightly deeper, and looks like frogm1's photo (except for the mottled bluing). This carbine in NL350 is all STD PRO, and had no cartouche nor acceptance proofs, and is registered with the Feds. You cannot "buff off" a serial number, it's too deep. It would have to be ground off, and like the other examples shown in this thread, grinding is clearly visible.