That would be against federal (and some states) regulations.
You can't make a new hi-cap from replacement parts. Yes, all the parts may be individually available. Yes, you won't get caught, likely.
Unless, of course, you go on public BBS forums like this one and start asking how to do it.
Personally I don't care what you do or don't do with your guns or anything else in your life, but be forewarned that what you are contemplating is illegal, and is off limits on this board.
