Single Six bore diameter

[xtratoy]

What year did Ruger make the 22 cal bore larger to accommodate the 22 Mag round.

 

[JCW64]

I'm pretty sure it when the 22 mag Single Six came out in 1959.

 

[street]

Years ago when Ruger first came out with the .22 Mag. Single-Six, they said that they could install a magnum cylinder on any Single-Six after serial number 150,000. That should put it in late 1959.