Yes, in a sense it was done many years ago. The .204 in essence is nothing more than the .222 Rem. Mag with a 30^ shoulder(couple other moinor differences also). But yes, I also know of a few guys that have necked up the .204 case and had dies made. I'm not sure if any die company at this point has a .22-.204 dies list as a production item or special order.
Dies and Brass are availe for the .222RM however.

Dave

 

If you used a .204 reamer with a .223 pilot you would end up with a .204 chamber with no neck. Just buy a .222 Mag rifle and you will have what you are wanting to build. Larry

 

A neck reamer can be used to bring the neck into spec.

 

Guess the effort and money isn't worth the gain. The bolt face on the Ruger Varminter I have looks like it would be easy to open up for the 22 BR so I think that is the route I will go. Thanks for your inputs.

 

I built one a couple of years ago and it's a great little cartridge. I'm running 40's at 3900 out of a 22" 9 twist barrel, add 2" with a 14 twist and 4000+ should be easy. PTG has the 22-204 ruger reamer. This is a simple wildcat with with a good supply of brass from a variety of manufactures. No fire forming or complicated caseforming and has substancial returns. I use a 204Ruger Redding Type S FL Bushing die with the Expander ball and bushing swaped out to 224 I load the 22-204, 6mm-204 and 25-204 with the same die, just swap in the correct expander and bushing. I did have to relieve the neck openning in the die to clear the larger cals.

AWS