I cast and shoot huge numbers of .22 bullets. The moulds I use are the RCBS 55gr. for most rifles, and the Lyman 45gr. roundnose for the 1:16 twist Hornet. I don't see that they are any harder than anything else, in fact it's easier because the moulds don't overheat. I just run the pot pretty hot, use mostly wheelweights with a touch of tin, and water drop them to make 'em hard.
Depending on the twist rate of your rifle, you may be able to get very good performance with cast bullets. The 1:16 Hornet can be run at full throttle, 2600 fps, the 1:14 twist .223 can go to 2400 fps and the 1:8 .223 goes to 1750 fps with good accuracy.