Proabably won't find a .204 in semi auto and the only 17hmr's that are in semi auto are, that i know of,Remington 597 <-----JUNK, and the Converted 10-22mag to 17hmr. It would be pricey to buy a new 10/17 already converted. You can get them from Volquartzen or make one yourself.

I personally would go with a bolt action 17hmr. like a Marlin, CZ, or Savage.

The .204 is a very hot cartridge and good for varmint hunting, but a 22-250 or .223 might be a better choice in ammo selection, price, and i would worry about the barrel washing out (wearing out rifling) in the new .204. 4000fps+ seems a little too much for such a small diameter bore to handle if you plan on shooting a lot. JMO.

Chris