I cast my own lead bullets that I powder coat and I also use the lyman type m expanders. I'm guessing you bought Lyman #: 7349053 If that one is too long and you can't adjust it deep enough for the shorter 458 socom brass you might have to buy a 2nd 45 cal shorter one and swap out the center expander. The ones for 45 win mag and 45 colt might work because those cases are shorter.
Another thing I've noticed is if I adjust the seating die like the instructions say sometimes I'll get the shaved lead ring too. That's because the crimp inside the seating die is squeezing the case mouth down before the bullet is fully seated. To bypass that crimp you need to adjust the center screw on the seating die almost all the way down. To get your seating depth close you have to adjust how much the entire seating die is screwed into the press. Once you get close lock down the die into the press and then use that little bit of adjustment you left in the center screw to get the bullet seated exactly where you want. Usually when you do this the actual seating die wont end up being screwed into the press very much. Sometimes only 4 or 5 threads, but that's still plenty enough to hold it in the press while bypassing that internal crimp.
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