Loadbooks USA make a set of load manuals for Contenders, there are two volumes. You can get them about anywhere, mine came from Midway USA(they are online, too.)
The Complete Reloading Manual for the Thompson Center Contender Vol. 2 starts at 30 calibre loads. The info is a little dated but, so is a .30 Herrett.
Start a minimum and work up- I bring mine up in 1/10th grain increments but, I live near the range.