83 rpm?

[Roller]

Figure this one. Don't think it's a bubble. Looks like a partial reverse?

[enamel7]

I see a lot of corosion there that could cause that.

[jfines69]

I see corrosion and that could be a die chip in the center of the MM!!!

[mustbebob]

Looks like the mintmark took a hit, and that there is a plating tear to the SSE of the mint mark. Since there is also a burst bubble to the east of the mint mark, we know the plating has been compromised.