I have 2 Blackhawks

[hittman]

Perhaps …..

 

[chet15]

Just scroll down a little further.

You can view approximate starting serial number (by year) for products prior to 2000 using the selection box below.

serial numbers will only show up on this particular page "IF" the number was digitally entered onto this system. I have not been able to research any individual serial number older than 1976, and from 1976 to about 1984 it is real iffy if those will show up as well.
So if somebody wants generality, they need to look at Ruger's yearly charts of dates of manufacture.
Just google "Ruger Single Six Dates of Manufacture" (or whatever series).

 

[weaselmeatgravy]

OK, It's becoming clear as mud. It's a 5 1/2 incher.
So a L.R. cylinder would likely be correct.

Well, it would at minimum have a LR cyl. It may very well be a convertible that is also missing the WMR cyl.

At that point, the single cylinder guns were pretty scarce. A letter would be the only way to know for sure.

In the mid-1960s period, your gun would be either a RSS5X (convertible) or RSS5W (single LR cyl). They started using the W, which in the XR3 days stood for Wood grips, to denote single cylinder guns in that early XR3-RED period. I have RSS5Ws in the 38xxxx and 39xxxx ranges and also two in the 82xxxx range. But there should also be a few in the 4xxxxx range.

Inconsistency was the only consistent thing about Ruger's catalog numbers and serial numbering.