Ok, I'm confused.
You mentioned a NM (New Model) Single-Six Magnum in your first post. You place it's manufacture in 1978,, approximately 5 years AFTER the OM's are all gone. When Flategate mentions the fact that the Magnum ONLY Single-Sixes were stopped in the 1960's,, you came back about an Old Model in your second post.
Which gun are we talking about here? One gun? Two different ones?
If you have a NM, and it only came with the 22 Mag cylinder,, it's a safe bet it HAD a 22 LR cylinder when it left Ruger.
If you have a OM Single-Six with the markings on the mainframe as "22 Magnum" then it USUALLY didn't come with an extra 22 LR cylinder.
Help me clear up my confusion.