Thanks guys! I will never sell the gun, so I'm not disappointed that it's not a Mark I.
The only thing I knew about it was my father bought it right before he was deployed to Okinawa for Vietnam. Probably his first gun purchase. Cool stuff! Thanks again.
I don't know how to measure BBL length, but from end to end it's 8-3/4" and 3-1/2" from end to front of body of the pistol.
Has fixed sights
Writing on frame says "Ruger 22cal long rifle automatic pistol" on left side. Right side says "Sturm, Ruger & CO. Southport, Conn., U.S.A." And of course...
My father just recently gave me the very first gun I shot when I was 10 (30 now).
I believe it's a Mark I. Serial #408537. I don't know anything about Rugers (I'm a Walther guy) and tried doing research online to find the year.
Since 1966s the serials are 406740 and 1967s are 436226, does that...