I don't adjust the expander/decapper, unless it's not popping primers out properly (rare with any rifle die, the way that I set them up - don't think I've ever needed to with 7.62x54R).
I insert a (lubed) case into the shell holder and raise the ram with the die installed far enough that the expander will enter the case. Then run the die in until it hits the case mouth. Adjust down from there, until the die starts trying to resize the case body near the web. If it's sizing enough of the neck to make me happy (at least 3/4 of the neck), then it's good enough.
If not, then that die may not work; because if it actually squeezes the case body to size it, the shoulder gets pushed forward slightly. And, of course, pushing the shoulder forward is likely to screw with headspace.
If I were wanting to neck-size as much of the time as possible, I'd probably just buy a neck-sizing die or a collet die.
