H & R Had many M-16 rifles stored in their factory with no serialization, the story I was told that during their contract with the US Government a bunch of rifles were rejected for various problems that were non-repairable to the lower receiver. Some of the museum guns had broken rear trigger guard tabs, others had front pins that were broken, ETC., all came out of the museum, with defect tags on them. I know for a fact that the damaged M-16's were repaired for commercial sales , as well as the M-14's and the Rare R-14's that were sold out of the museum. The M-16 rifles with no serials were numbered by H&R to replace damaged M-16's returned because of the defects-- The three digit serial number M-16 was hand stamped at H& R for them to sell it. If you could see the original sales form it would say 1975 and H&R M-16. I personally worked on a lot of the H&R Museum guns that were owned By R.J.Perry--- If you need any questions answered PM me please !