Your gun is an antique, therefore not a firearm, per ATF rules, so I doubt you are risking a charge of owning a illegal firearm with no frame stamped serial number. If the butt cut for attaching a shoulder stock caused the removal of the original serial number, than all you have is an antique S&W with no serial number on the frame. If the stocks are original, then the serial number is on the back side of the right stock panel. If the gun has parts that were rejected by the Russian inspectors, then the serial number may be on those parts, as S&W often reused parts from rejected Russian contract guns to complete assembly of commercial guns. If the gun has a butt swivel and a slot cut to attach a shoulder stock, then I strongly suspect the butt cut is after market and not factory. Ed.