Sounds like a great project! I have often lusted after the idea of a double rifle in 22 Hornet.

As far as regulation goes, just pick the ammo you like. I know that the 2 time defending Texas State Champion in .22 metallic silhouette used a Contender match barrel with a Leupold scope and Winchester Western Wildcat over the counter ammo.

When you get to regulating the rifle buy all the .22 ammo in the same lot. I figure you don't need any more than 10-15 thousand round! I mean if you are like me you'll shoot the heck out of that rifle!