I can think of dozens of reasons why such a gun would be totally impractical or extremely expensive (I am talking thousands of dollars, not hundreds). But "great ideas" don't sell. All I can say is, raise the capital, make a working model, then peddle it around to the gun companies, or tool up to make and sell it yourself.
IMHO, this is another case showing that just because someone can think of something doesn't mean that it would be practical to manufacture or profitable to sell.
Jim