Should I buy ?

[street]

Finely got a hold of someone in records and the person I talked to told me this 22 was MFG in DEC. 1964 8) and yes it is a duplicate but could not tell me why Ruger did this but thats ok some info is better than none.

Ruger always assigned certain serial number ranges for certain models. They did that with the .22 Autos, as well as the Single-Sixes. When Ruger started the Super Single Sixes, they started at 500,000. At that time the Single-Sixes were either in the 300,000 range or the 400,000 range. When the Single-sixes got up to 499,999, someone at the Factory forgot that they had already used the 500,000 range for the Super Single-Sixes, so they continued the Single-Six into the 500,000 range. They didn't catch it until a few thousand frames were stamped. So instead of destorying all of those frames they stamped a "D" in front of the serial number for Duplicate. What you have is one of those guns. There is also a Super Single-Six out there with the same serial number, with out the "D". Good luck finding it.

 

[street]

4 years later the Single-Six SN's finally caught up to the 500,000 block of numbers assigned to the Super Single-Six, and about 50K Single-Six guns were produced with the same SNs as the Supers. By this time the Government had mandated that each firearm at each individual manufacturer had to have it's own unique SN, not just a different model designation. To comply with Gov. Regs. the Single-Six guns with "Duplicate" SNs were stamped with a "D" and the SNs were jumped to the 800,000 block, soon after the prefix numbers started to appear.

Thats pretty much how I understand it.

Your time frame is a little early on the Gov. requiring a unique serial number for each gun. To comply with that law is the reason that Ruger started using the digit pre-fix serial number system. These guns in the 500,000 range was a little early. They put a "D" on the serial number because it is a duplicate serial number. They put a "D" on some of the Single-Sixes in the 100,000 range, because they were duplicates too.