weird proof half?

[brendan1414]

I found this 1979 s half dollar. I'm assuming proof because it has the San Fransisco mint mark but I just can't see this ever being a proof. Has some weird bump on the back that is concave. Copper edge. Any inputs on this?

 

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[enamel7]

Definitely a proof. Bump looks like it may have been heated at one time.