Don't worry about it. When you finish shooting clean it easily:
Blued guns: Use Shooters Choice Bore Cleaner on cotton cloth wrapped around large flat eraser. Use old toothbrush dipped in SCBC to clean rear barrel protrusion and inside frame. The black comes off quickly.
Stainless guns: Use Shooters Choice Bore Cleaner on Lead Away cloth wrapped around large flat eraser. Use old toothbrush dipped in SCBC to clean rear barrel protrusion and inside frame. Cleans black away even faster than above. Do NOT use Lead Away cloth on blued guns as it WILL remove bluing.