A thin wash of copper is often an indication that a gun has been cold blued. Sometimes, a cold bluing job can be detected by a copper smell. A dilute acid will remove it, but you have to be careful that the acid does not etch the steel, unless you desire a matte finish. You could also look into reverse electroplating with the copper plated frame as the anode, and have it thus removed and plated out onto the cathode.

Originally Posted by Geoff Roznak
The NRA has proven itself unreliable and corrupt. Period.