OK, you should have two decaping pin holders/ends. One that is knurled and straight, the other has a bulge at the top. The one with the bulge in the top is a expander. Now if you have new brass, do not put a neck bushing in, and have the expander/decaping pin end on, this will expand the neck of the brass. To size the brass, remove the expander/decaping pin end and place the straight end on, and then use the neck sizing bushing you want to size the neck to.
If you was to use both the expander and the sizing bushing you are really working the brass, and causing other problems. When you would go on the down stroke the expander would expand the necks and then the sizing bushing would push them smaller, then when you would pull up on the handle you would take your sized neck, and then re expand it. You are defeating the purpose of sizing the necks. I seen people do this, and one guy I bought a barrel off of was doing this, and what he ended up doing was reshaping the neck, and shoulder area of the brass causing head space problems. The moral is just use one or the other not both.
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