Try...
55 Grain Sierra Blitz King and N-135... advantage of .222 RM is you can use slightly slower powders than in .223. In a way, you almost have to... Disadvanage is that the Rem. brass is a bit soft and won't take the pressures that, for example, Winchester .223 will without losing primer pockets. So to get roughly the same velocity (as a practical matter the two are a ballistic standoff) you use a bit slower powder at slightly lower pressures... Wouldn't a .222 Rem Mag Ackley improved with some good tough brass be interesting??
Incidentally, although based on the .222 Mag case, the .204 has had the shoulder moved forward to add powder capacity and allow for a shorter neck in conformity with current thinking. So just necking it up wouldn't give you .222 Mag brass. Base to shoulder on .204 Ruger is 1.539"; on .222 Mag is 1.464". So if someone were to neck the .204 UP to .222, there would be the ".222 Super Mag." Anybody want to try this??
Seriously, it's good to see some folks who still love this oldie. It's one of my favorites, and my first real varmint rifle (in 1966.. a Sako Vixen) was a .222 Mag. Still have it. Also a Hart barreled 700 and a 40XB repeater with 8- twist barrel.. All shoot better than I can.
I think the .223 killed the .222 Mag because the .223 was adopted by the military.. and the .222 Mag is a bit too long for the AR15 action and magazines.. And all the hoop-la in the 60's and 70's favored the .223... one had to give and it was the .222 Mag. Too bad....