Steve,
I'm with you, don't worry about it. If you have the enthusiasm to make it and it makes you a living, go for it. If you built complete guns, you'd likely eventually be sued for some idiot blowing one up or shooting his foot. Pursue your dreams. This is another cool project and you are obviously well qualified to do it. I'm in awe. I'm qualified to turn a handle, so I have a good appreciation of the work involved, but I couldn't do this project.