As DWalt stated, the BATFE considers it to be a firearm once the serial number is applied to the frame. If, as someone asked, a frame was damaged during the assembly process, it could not be scraped without reporting its disposition to the BATFE.
As is evidenced by the production of the .22/32 HFT's, wherein each completed gun received a numbered pair of two screw extension target stocks in order of the guns completion, there is no correlation between the sequence of serial numbers and the sequence of stock numbers.
This is not to be confused with the serial number applied to the inside of the right stock panel but an assembly order number stamped on the bottom of the left stock panel. This was done for about the first 3,000 guns assembled and really shows one the randomness.
You must realize that groups of frames were handed out to the various workers and assembled in no serial number sequence and some workers may have worked faster than others. This creates a very random pattern of gun serial numbers and then the completed guns went into the vault in preparation for shipment.
As an order was filled, a shipping clerk would go to the section were the needed model was stored and grab 10 guns. No care was taken to grab 10 sequentially numbered guns as they were merely filling an order with inventory. The serial numbers were recorded as they went out and it is these records that are used to obtain shipping dates or information contained in history letters.
All of these factors tend to add to the randomness of dates and serial numbers and drive us collectors, who want things all neat and orderly, crazy.
