it depends on which one of their guys built the gun.
if you look at enough of them you can see clearly the workmanship varies from gun to gun.
a bunch of us on the Rossi lever gun forum [which is back up and running BTW] speculate that one guy builds each rifle from start to finish, mostly based on the fit and finish of the various guns we own.
what he has there is a pressed down portion of the front sight making an impression in the barrel.
it's no different than rolled engraving or a rear sight, or a too tight barrel in the frame on a revolver.
except that it's miniscule and waay down the barrel after the point where the bullet has gone through all of it's up and down sizing and spinny gyrations.
besides where is all the stripped off and galled lead?
all that's happening there is a small portion of the bullet is being squeezed a bit.
all on one side of the bullet, all at the same point in the process.
probably moves the point of impact a little, but it's moving them all the same.
kind of like a gas check coming off at the muzzle it keeps happening at the same time every time.