This is an old thread, but life is full of surprises and I just had one with my Bartz upper. As some of you know, I recently shot some all brass bullets through it and tomorrow being another range day, I decided to dry patch the remaining Kroil out and also check the bore with a scope. I had already cleaned it, while it was still warm, at the range after shooting those brass bullets, so I didn't expect to find much more than a little brass buildup, which I did. The brass residue did an outstanding job of illuminating the portion of the rifling that exerts the most rotational force on the bullets, much like copper does to a less brilliant degree.
Not too long ago, I told another member here something I've always wanted to see implemented in a 450b. Namely,
Polygonal Rifling, just to see what impact it had upon performance. Well, guess what that bright brass residue revealed, that which I never noticed with a totally clean bore. Sure enough, it has polygonal rifling. Brett never mentioned that to me when we were discussing his company's product. That's pretty cool! Makes my mind wander all over the place regarding how with some bullets, it behaves differently than my original Bushmaster upper, with its conventional rifling.
Its an accepted tenet that the more confidence you have in a rifle's ability, that more it translates to the rifle actually delivering better performance up to a certain point. At least that's the prevailing theory. (see sig)
The small amount of brass buildup is now effaced, thanks to some JB bore cleaner and Mr. Armstrong at the rod. Its back to being hard to notice the polygonal rifling as the rifling details are somewhat muted by the light from the scope reflecting back into the camera and causing the automatic gain control to reduce the sensitivity and contrast. I may just have to slug that barrel to produce a visible example to photograph for you all to see. The Lyman Digital Borescope has image capturing capabilities, but it doesn't do a good job as opposed to viewing the image in real time. At least, I haven't figured out how to enhance it when scoping a really shiny bore.
Just a FWIW for you bore technology fans.
Hoot