Firing pin groove

[Danjet500]

I've been under the impression that all lr cylinders had a groove in the face as in the photo below.

The lr cylinder on my Single Six does not have this groove. Both the lr and magnum cylinder look alike from the rear face. These are the orginal cylinders for this gun as you can see by the sn. I bought this gun in 1976 and have owned it since. Is this common or is the photo above typical for earlier models?

 

[flatgate]

My most "current" New Model Single-Six does NOT have a firing pin groove on either cylinder.

flatgate

 

[mattsbox99]

Transfer bar guns do not need a firing pin groove in the cylinder. The firing pin is retracted when the trigger is released.

 

[Hondo44]

+1 What flatgate and mattsbox99 said.

Someone at Ruger fnally realized the groove was no longer needed some years after the NM intro so the change doesn't correspond to the OM/NM changeover.

This early new model #62-29675 from 1973 still has a firing pin groove in the 22 LR cylinder. Also it came with a fluted 22 Mag cylinder (another non-OM/NM change) since they continued until c.'76. Both of my stainless SSs, one from '75 and the other '76 have grooved LR cyls.