I masked mine by dripping wax around the points that I did now want paint to get to. I then used a flat dull blade (a flat head screwdriver with a fine point) to gently scrape away the extra wax around the trade marks. I think it worked quite well. I also did a full disassembly of the receiver (removal of the selector switch, bolt catch, ect ect) to ensure that no parts became jammed or stuck by the paint. I painted the inside as well as the outside using Krylon mat black paint to ensure that even if there was scratching on the outside of the receiver the black color would be maintained. Here are my results.