ML barrel question

Just wondering if after a period of time with moderate use, does a ML barrel develop a scorch mark just beyond the breach?

I had never fired a ML before three years ago. I sighted the gun in during the October. Being a total newbie I put the gun away until the ML season in Dec. I was shocked by the amount of corrosion in the barrel. I cleaned it several times immediately that fall. I thought I'd removed all blemishes.

Now I notice a few hard to see blotches in the barrel just beyond the breach. I know how to clean the gun properly now and the blotches haven't gotten any worse over the past 3 years. I'm wondering if ML barrels develop some scorching with use??

just keep it cleaned, inside and out, and well oiled during the off season