"at least 69 years old"
It most likely would not be a convertible, and a MAGNUM Cylinder would be a no go.
The barrel ID was smaller.
Post your Serial Number#, you can XX the last 2 digits. This will get you some more accurate info.
-OR-
A fairly easy way to determine if a Magnum would be safe.
Use the shank of a 7/32 drill bit as a Pin gauge.
If it go's in your good,,,
if it does not go in,,,
it's meant for 22 LR/L/S only.
MAGNUM CYLINDER:
Can and will it work, YES!
Just not designed for it!

Just buy some CCI Velocitor.
As for the Box saying "Blackhawk"
Sounds like you have a Single Six in a Blackhawk box. Wrong Box for the Single Six, but there are others that will probably trade you for the correct box.
Or sell the Blackhawk box and buy more ammo!
