Well, yes, but when I am making a one off receiver, I do not care as much about machining time, as about how much time would it take me to make one off fixtures, reclamp everything, touch off the tools, align etc.
So, if it would take me 5 hours of machining time to make a receiver, but only one personal hour, it is a better deal than 30 minutes of machining, but 3 hours of making custom fixtures and clamping and reclamping and dealing with mistakes.
Anyway, I admire your plan and am looking forward to seeing how you make that receiver. I am getting an itch to make something like that as well.
i Not speaking from any actual knowledge, of course.