Odd 'step' in the bore?

[Woodsy]

The Stellite liner is the most likely reason. As a gunsmith I have never found any need to own a bore scope. If something in a barrel is not visible to the trained eye then it is not likely to ever be a problem. I have had many customers over the years (that have purchased expensive bore scopes) come in to have non-existent problems "rectified". The only common problem that is not easy to see by eye is a bulge right at the muzzle, but it is easily detected with a bore plug gauge.