Screw the sizing die down until it touches the shell holder, then back the die out about half a turn. A regular 8X57 die works perfectly, as the only difference is the rim.
Be sure to lube the inside of the case neck, as well the outside of the case.
Resize the brass in the die and try it in the rifle. It will not likely close on the case, as the brass will not be fully sized for the chamber yet.
Turn the die a bit further down and try again. Do this until the rifle closes on the brass.
Once you get the die set properly, lock it in place. You are now ready to resize all the brass.
Now, the first time you size all the brass, partially back out and rotate the brass 180 degrees in the shell holder, and run it all the way back into the die again. This will insure that it is sized properly and you will have no trouble chambering it in the rifle. You only need to do this on the initial reforming.
Let us know how you make out.
Ted