We have in our police inventory an ancient Colt SP1 AR15. It was purchased by the State in January of 1965, for (can you believe) $131.30.
The serial number is SP021XX. It has been unmodified, and is in its original configuration. Whats really strange is that the rear of the lower receiver has a small hole just in front of where the buffer tube screws in. Inside of this hole is a small roll pin. The selector also has a hole drilled through the center of it. The bolt carrier is manganese phosphated, but the bolt itself is chromed. The only markings on the barrel are a "w" on the barrel side between the front sight tower, and a "s 12" on the underside of the barrel near the flash hider. I think it would be safe to assume that it indicates a 1/12 twist barrel. Would it also be safe to assume (by the serial number)that this was the just over the 2100th AR that Colt produced? Any comments would be welcomed. I have the opportunity to purchase this weapon, as it is being retired (NOT for $131.30). Thanks gentlemen.