Hoppes #9 is ammonia based so is unwise for use on nickled guns. If the ammonia gets under the nickle plating it can destroy the copper undercoat and allow the plating to flake off. I use #9 for blued guns and Breakfree or "Miracle cloth" to clean the bore on nickled guns though it takes a lot more elbow grease than #9.

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Big bang, much smash'em.