Some bore cleaners warn not to leave them on nickel finshes-will chrome lined barrels be damaged by some bore cleaners?

Yes, some cleaners can harm chrome lined bores. Basically, just don't use any concentrated ammonia based bore solvents. Actually, for a chrome lined bore, Shooters Choice (regular bore cleaner) is about as powerful a solvent as you need.

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No.

You wont hurt a chrome bore by using a bore cleaner. Even those with high ammonia concentrations.

However, do not allow such solvents and bore cleaners to contact your aluminum receiver or other aluminum parts, as they will attack the nickel accetate sealant applied at the factory.

If it does, simply wipe it off followed by a good oil or CLP which will negate the corrosive effects. Or better yet be very careful when using such bore cleaners or copper solvents.

As A_G pointed out, Shooters Choice works well and is what I use, even though it is mild compared to some products. It recommends right on the bottle to avoid contact with nickel surfaces.

If you let amonia based solvent sit in the bore long enough it will turn the chrome black in color normal cleaning is fine just dont let it sit.