I don't think it's been on fire. Coin has thin rim, it's not completely gone. There are some what seem like a ver small bump behind the head and what seems like a metal loss/
Cud on reverse exactly opposite of that bump. And long semi circular curve raised portion running in front of bust. Please see the images above.
Having said that I could not be 100% certain about the diameter. I need to find a better way to take pictures, if I'm able to do so, I'll share them later.