The pin latch pushes in from from the left side.
I just had never had that kind of problem with a single action before. Every other one I've handled or had, the latches always held the pin in securely.
I figured either the latch or pin was worn and after some more research, I found it isn't...
A friend of my son has a blued Vaquero in .45 Colt that after firing a single round, the base pin comes out 1/16 to 1/8 inch and it jams the action so it will not cock with out pushing the base pin back in. One time the base pin backed out and the base pin latch jammed along with the base pin...
The M77 MK ll requires rings that are different heights, the rear taller than the front.
Look at the following link for the correct one for your application. Ruger ring chart
It was made January of 1983, not drilled or tapped. Not sure if the box should be plastic or cardboard, I inherited the pistol from my Brother without box or manual.
Thank you all for the replies
I have a single cavity round ball mold of unknown make (maybe Lyman) to give if someone has a use for it. The only marking I find on it is 411 on each mold half. It's never been used, slight rust from neglect in storage, fully operable. pm me your info if you want it and I'll send it.