New M10-5, need born on date

[maxwell]

Found a lonely M10-5 4" heavy barrel at the local pawn shop. Heavy holster wear at the muzzle, but tight lock up. Magnas and a Tyler T grip.
High serial for a -5, D863,xxx. Curious how late in the run it came from.

 

[Targets Guy]

Probably 1976. They topped out of the D's in 1977 at D999999 and the Model 10's went to 2Dxxxxx

 

[lamarw]

I am guessing closer to 1975. One of my 10-5's has the serial number D867104 and I think it is of 1975 to 1976 vintage.