Looks like some un burnt powder hanging in there. I have the same problem in my 22mag and 17hmr. The scary thing was I found it building up in my suppressor. To my surprise I took the suppressor apart and cleaned all of that out and lit it with the lighter it it did indeed burn.
Most Importantly, how does it shoot?
Oddly that is the color of the powder used in 17 HMR and 22 MagIt doesn't look crowned to me, just a recess to an uncrowned end of the barrel. That stuff in the barrel seems like the wrong color for un-burned powder.