You can find out how old an HS Model 10 22 revolver is by taking it to a local pawn shop or gun dealer. You can also use publications that are written to help identify the age of a revolver.
That 22 revolver is IJ targeted sealed made in Pittsburg, Ms.
The year a HS model 10 22 revolver was made should be stamped on the metal below the barrel on the left hand side of the gun. This will be a bit ahead of where the grip begins.
You can find a 22 mag cylinder for a 22 mag revolver mod 21S MIW Germany on eBay. You may also be able to find one through antique sales and antique gun collectors.
@ 75 years old
Call Colt
http://www.gunpartscorp.com/forum/
Ruger website, customer service, historical data, revolver, single six, find your serial number.
Pre 68
Blue Book of Gun Values
You must call Colt to find out.
IF the revolver is marked ".22 LR" yes. If it is marked ".22 WMR" or .22 Mag" or " .22 WRF", then NO.
50 yrs old