We use and sell Gun Scrubber at the shop. It works very well. Just don't let it sit on your skin very long. It will make the skin peel. I got some under my wedding band one time, couldn't get it off fast enough, it hurt.
On the other hand, a wedding band can be painful under any number of circumstances.
One more word of caution about W-D 40. It will remove nickel plating. I saw a plated S&W Mod. 27 cylinder that had been soaked overnight in a bowl of W-D 40, half of the plating had peeled.
Ron