The reweld projects in the US use closed bolt operation, with a semi auto only trigger mechanism. The operating system design is developed. A Cdn. gun would need a new receiver, and this is the hurdle. Economically whittling a receiver out of a block would be quite a challenge. I suppose that starting with a precision casting would reduce the size of the pile of chips somewhat.
What would be the size of the potential market? At what price? In Canada, could 500 $5000 units be sold? Could the things be exported to other markets? What is the supply of good Brens from which to harvest parts like?