Yep, I tried it. I never blued anything before. I am going to leave it at this because I am afraid I might mess it up. Next time, I am going to try it with a stripped receiver. Before I add anything to it. I think it might work out better. Also, I am going to ignore the step that requires you to wash it off in water. All this surface rust is a pain to get rid of.
This is an East German kit with a Yugo UF stock on it. I blued the underfolder too cos it was all worn. The stock came out better than the receiver.
The valuable lesson I learned from all of this is that Krylon BBQ and stove paint cannot withstand the mighty cleaning power of Rusty Duck. lol.
Here are some pics. The flash from the camera produced some light spots but the bluing is all uniform.