Check for a little lead slug rattling about inside when you open her up.
Anyone squeezing off a few rounds in your neighborhood ?
A good metal fab shop could TIG and grind it for you too for a couple of bucks

 

That was my first thought, too. Looks a heck of a lot like a .22LR to me. I'd definitely take a look around inside for damage and lead.

 

ahh my fellow shootist concurs ........ so chances are you have a round in there and
a few bits of shattered casing bits on the bottom also

Looks like a ricochet upward from the ground hence the wide hole from an already
impacted small caliber round .....doubt there'd be damage inside as the energy would
have dissipated by about 2/3rds once through the case and from the ricochet


And if it is a slug hole and you were on the bike when it happened one word for you "Lucky"

 

gotta love ballistics.... they just dont lie....