Are you referring to the front of the cylinder especially? I also like to keep that clean. I found that lead remover cloth usually works well. Before I discovered that, I once took the cylinder off my GP100 and soaked overnight in Hoppes solvent, but that was a bit of a pain to do.
I have 2 sp101 would like to clean the carbon residue
Very good on Stainless, but will remove bluing on blued guns....
I was picturing the OP's SP101 as stainless, but good point.
Man, you must use a lot of Flitz. . .Just be careful using any type of abrasive like Flitz or similar n\because then you're messing with the cylinder gap spacing
LOOKS LIKE YOU WAS SHOOTING BLACK POWDER
ANY metal abrasive will do that; and BTW, it really doesn't take much when you measure gaps in .001 increments; Americans always like to think more is betterMan, you must use a lot of Flitz. . .
I don't think I'll live long enough to polish the cylinder gap open appreciably with Flitz, 6 days a week and thrice on Sunday.