Here's a quick link to a page on the Chuck Hawks site for adjusting dies.
You are reloading .357s at the moment with this die set?
The expander die is fairly simple to set up but easy to go too far with too.
-Put a resized case in the shellholder and raise the ram up to the top of it's stroke.
-Next, thread the expander into the press until it's just touching the top of the case.
-Tighten the lock ring and cycle the ram again...one full stroke.
-If the case mouth isn't expanded enough to get the bullet started in the case without "shaving" some material off, loosen the lock ring and lower the die a small bit...I usually go in 1/16 of a turn increments.
-Cycle the press again and check if the mouth is belled enough to start the bullet. If not, repeat lowering the die a hair & check again.
-Once you've got it expanded just enough to get the bullet started, lock the ring and try another couple cases.
If your cases are being expanded erratically (some more than others) use a caliper to check the length of the brass...they may be different lengths and need to be trimmed to uniform length. Uniform length is a big key to uniform expanding.
Are you loading jacketed bullets or cast lead?
If cast lead, you'll have to expand the case mouth a little bit more than for jacketed bullets since cast lead bullets are usually .001" larger in diameter than jacketed bullets for the same caliber. (.358" vs .357" in your situation)