sirsloop, look closely at your before and after pictures. I suspect you were a victim of what I call the "fulcrum effect." The before scope mount extends beyond the point where the barrel taper starts--the fulcrum. The pistol recoils and the barrel and its rings & mount want to stay at rest--Newton's Law. The effect is a counterclockwise rotation of scope, etc., centered on the fulcrum. The front of the scope, etc., wants to move down, and the rear of the scope, etc., wants to move up. That gives back and forth sheer force due to recoil and up and down force due to the fulcrum. The result = sheered screws.
Notice the after picture and how SKS eliminated the fulcrum effect via a moulded-in block on the bottom front of their mount. It touches the barrel at the rear and at the front.
Your mount also did not perfectly match the contour of the barrel. In the before picture notice the lines where the edges of the mount marred the barrel above the chamber. In other words, your mount sat on its edges on
top of the barrel instead of
on the barrel. I'd be willing to bet that the SKS mount is a perfect diameter-match to your barrel radius.
You could have eliminated the imperfect diameter-match with emery cloth on the mount with the barrel as a guide. Then a thin coat of epoxy between mount and barrel would have given extra sheer insurance.
You could have eliminated the fulcrum effect via a 10-32 x 1/4" or 5/16" set screw through the front of your before mount and just touching the top of the barrel.
But who knows. SKS is in business for a reason.
