To CmdrSlander: I've got to ask, do you have any manufacturing experience? Have you gone as far as to consider how you are going to design the parts, fixture the parts, machine the parts, and so on and so on, all the way to distributing them to the customer?
I'm not trying to be a jerk here - I'm genuinely interested - but the comment about making the receiver and magazine tube either integrated or separate raised a yellow flag for me. (I am assuming you did not mean machining a receiver and magazine tube out of a solid billet material, which from a manufacturing perspective would be suicidal, and also cost prohibitive to the end user...)