All videos or posts on removing the buttstock of the M77 just mentions a long screw driver. We'll I've locked the thing in a vise and using my 11" flat head screw driver cannot for the life of me get the screw to budge. I let some penetrating oil soak from the top and bottom and still nothing. They didn't start using some type of thread locker on these screws did they? Thanks for any pointers or tips!

My M77 had a metric hex bolt. Can't remember if it was slotted for screw driver or not. Can you try a socket wrench?

Mine also had a hex bolt. Are you sure of what you're working with? You should be able to see it with the rubber butt pad removed.