As others have indicated, there were (are) no Mark I Model 77s. What makes this fact odd, in addition to the usual practice of II following I number sequencing one usually assumes is the case, is that Ruger dubbed the target version of their .22 semi-auto pistol the Mark I from 1951 thru 1982. In 1982, after some minor changes were made to the pistol, it was called the Mark II. A couple of years ago, after some more minor updates were made, it was renamed the Mark III. But, as Art Eatman noted, it is rather unlikely that Ruger renamed the original Model 77 "posthumously".
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