I made myself a square tapered reamer so that I can drill the ramrod hole 5/16", and ream it out so that it's 3/8" at the entry, and 5/16" at the bottom.
7/16" would be an enormous hole. Draw out your design on paper, lock, stock, barrel, ramrod, etc, and you'll see how incredibly thick the gun would have to be to accommodate that 7/16" ramrod hole.