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Ab_member
I doubt I'd trust the precision of the Harbor Freight mill for a receiver. disclaimer: I am not a machinist, but would love to learn the trade, therefore my opinion is based on previous experience with harbor freight tools and quality of forementioned tools.
Just an FYI - there are gunmakers in foreign countries that cobble together guns with little more than hand tools. So pretty much anything can be done it is just a matter of how much time and effort you want to put into it.