Scope ring broke

[Axis II]

I have a very old set of weaver rings that the top ring slides into a notch and tightens down with flat head screws. I pulled the rifle out to put Burris z rings on it and heard metal hit the ground. The cross bolt that goes through the base snapped off at the screw head and the piece of the ring was gone. Never seen anything like that before. They were installed using a Fat wrench too. Good thing I bought the Burris rings to change the weaver.