S&W made a half-million 4th Change revolvers before entering the WWII production years. Even those million WWII guns were technically all 4th Change as well.
The value of a poor finish M&P from this era is very low, with little prospect or gaining value, so what you do to the gun is not going to hurt the value of a beater anyway. Removing nickel can be done in a couple ways. A reverse electroplating process is one way, which is not normally done by individuals. The second is using a heated chemical bath using B-9 nickel remover, where the nickel is dissolved over time. It requires submersion in 120-150 degree solution for a few hours.
As far as I am concerned, all the room temperature options are not worth your time or effort. They just don't work that well for me, plus some will attack the steel as well. Either send the parts out and have a professional remove the nickel or use the heated solution route.
Bottom line is that you will end up with a matte surface discolored steel and will need to carefully smooth and buff to get a gloss blue. I would not recommend cold blue for a revolver that is going to be carried or shot lots since none will give you the durability of a professional blue. Birchwood Casey is not the way to go as there are better cold blues on the market. I prefer Brownell's Optho-Blue Cream.
Bottom line is that it will not improve the operation of the revolver. It will not add any value and it will take a lot of your time to complete the job. How about finding one in better condition or already blued and buy it if that is what you want??
