Brownell's sell a special chemical stripper to remove plated finishes. This would probably be less damaging to the metal than most of the "home brew" type stripper.

BROWNELLS : BROWNELLS : ROOM TEMPERATURE NICKEL STRIPPER - World's Largest Supplier of Firearm Accessories, Gun Parts and Gunsmithing Tools

The best way to strip nickel is to have it DE-plated by a place that does gun plating.
They basically reverse the plating process and this removes the plating.
Note that you probably DON'T want to trust this to a motorcycle shop that does chrome plating. Guns are "different" and have different problems.

The "watch outs" here are several.
First, that some home made strippers can and often will do damage to the steel, which can be difficult to correct before refinishing.

Second, you have to get ALL the plating off, including out of the pores and all tiny crack and crevices. If you fail to get it all, when the gun is blued the remaining tiny specs will make the gun look like it has white freckles.
This is the remaining plating which won't blue.