I'm new to the board and have done a little browsing, I have yet to find any mention of the 204. I do find others like 220, 243,22-250 etc. Doing a comparison of the 204 to the 243 the 204 performs better.
Hornady .204 40 gr v-max, 3900 fps
Hornady .243 58 gr v-max, 3500 fps (guess)
overall the 204 shoots flatter, past 500 yds is faster and has more energy.
Just looking for thoughts.