Hey Bert, have a look here, please

[BPTactical]

It appears that this barrel was recrowned.
First guess is a non piloted crowning tool or a piloted one that seized up.

Second guess would be a false muzzle that was either too loose or spun in the barrel.
If it was the former there is no better testament for crowning with a single point tool, if the latter it's just poor form.

Curious what your thoughts are Mark.