jelenko
Gold $$ Contributor
You're welcome.This is what's happening with me. Thanks for reporting!
At the same time, the pics of your bore show the middle of the grooves much lighter color than the parts of the groove next to the land. You were wondering if the darker color was the unworn nitride finish.
FWIW, that is probably not the nitride finish. My understanding is nitriding penetrates several thousandths into the surface => unlikely that there is that much wear.
To check, just use Iosso/KG 2/Flitz bore cleaner on a tight fitting patch wrapped around a parker hale jag. Do 10 passes; replace the patch with new abrasive four times.
Cleanout with bore solvent, dry patch; check with borescope.
If it's carbon, you'll see a lot less of it and the center light colored area will be much wider.















