you will surely be safe using 30 carbine loading data. You can prolly factor an additional 100'/sec for the reduced neck size, maybe even a bit more since you're going down to 22 cal from 30, and then add in another 100'/sec or so for bullet weight reduction. If you're shooting a 40 - 50 gn bullet from that conversion you have dropped at least 50% of the bullet weight of the normal carbine load, and that adds to the velocity. HTH. Mikey.