I've never heard of it, but am hardly knowledgeable about such things.  The only thing that strikes me is the low ballistic coefficient of any bullet in that small of a caliber, unless you were shooting pencils.  It sounds like a crock.  .308 diameter did not happen by accident.  Also, "superior to all other calibers . . ." in what way?  Certainly not in ballistic efficiency.  I will go check out the site now.  

www.jamescalhoon.com/19caliber.html

Edit:  Okay, been there.  Why am I not surprised he is trying to sell you something?  Here is a quote:

From the site (bullshit department): Here are some more features of either of the two rifles, chambered in the 19 Calhoon Hornet: 250 yard range (100 yds. more than the standard Hornet, and more than twice the range and energy of the 17 HMR or Hornady Magnum Rimfire)

Better have good air/arty support.  

Like any good myth, there were bits of actual fact sprinkled in among the fiction...

Do some research on the SCHV (Small Caliber, High Velocity) studies that the military was doing in the late '50s and early '60s.  The .223 round was created by the father of one of our members ("Gus"'s dad: G. A. Gustafson) based on the .222 Remington cartridge and the SCHV research, which this article is trying to refer to.

-Troy

-Troy