I recently ordered parts kits for MP5 (9 and 40/10) and two reciever flats. I noticed that the parts kit's barrels are obviously less than 16". My question, if I bend and weld the recievers, since there is no serial, does it still require a stamp? If so, how can I do it with no serial? If no stamp is required, is there anything I need to do to protect myself from Uncle Sam, or does the fact it hasn't a serial proof enough? Thanks.