I thought the new win 70's were from FN and made here?
Anyway, I doubt the are chatter marks, as they are hammer forged .
I highly recommend staying away from firelapping. I ruined a barrel with it. Smoothed over all the rifling.
Best thing to do is get someone that knows how to properly handlap a barrel. Any gunsmith can.
You can to a point with bore mop and 600grit lapping compound.