I second the bravo.

On barrel surface prep, go for the properly struck finish of a fine brit double rifle, with walls right about at .090" in the oiled and rust-blacked finish.

I haven't chapped a set of double rifle barrels yet, haven't handled a set of properly-chooched barrels showing OSR optical evidence either, but in my few 40 years of time around engineering and machine shops I've seen distinctly local surface finish affect on plenty of service parts that had been taken through the limits of their material's modulus of elasticity, affect that might measure in the fifty millionths neighborhood on the inspection table, but signs that something significant had occurred in the material.
The fine quality and finish of properly struck and blacked barrel steel would seem to me to be a good canvas for that kind of surface-finish affect.

From my experience, when the metal's locally lost it's nature it'll often somehow show at the surface.

Simply pushing mono solids through a barrel might not have the same effect as running them at the pace of normal internal ballistics.
Think of the difference some sweet-tart's ass might feel between a stroke with a buggy-whip and a good crisp snap with the same searing tip.
She'll likely turn and 'change her temper' to some extent at the crack, it'll definitely leave a mark that'll change the local landscape too.

Firing a cartridge in a rifle barrel is a very dynamic event.
Similar to the buggy-whip and temptress's ass analogy, when certain thresholds of energy delivery are crossed, there can be amazing consequences.

Just putting that out there for thought.

Cheers
Tinker