Mike was talking about the expander button in the Full Length Sizing die. What diameter is it? If indeed, the expander button is .435" - it is more than .010" LARGER than it should be and needs to be ground down - do as Mike suggested, remove it or skip that stage and measure the case mouth after sizing.

I see from your post, you are guessing at the groove diameter.

You should Slug the bores to determine the exact bore and groove diameter. The bore, is the small measurement - the groove diameter is the "important" number.

Do not increase the diameter of the bullets until you slug the bore.

A soft lead slug is pushed into the bore - run a rod down from the muzzle to the slug, then one up from the breech to the slug. Thump one rod against the slug, holding it still with the other rod, then push it out and measure it with accurate calipers. The bullet should be that diameter or up to about .002" larger.