Anyone know what the production years for the 10-6 were?
And what about the 10-6 with the 4-inch heavy barrel? Were there a lot of those made, and were they made during the whole production run, or just for a brief period?
The Model 10-6 was made from 1962 until the end of 1976.
By definition, the 10-6 had the heavy barrel. The tapered barrel version was the Model 10-5.
I believe, although I can't prove it, that there were more 4" guns produced than any other length, during the 10-5 and 10-6 era. And yes, they were produced throughout the production period.