The dies merely 2 different die bodies used for expanding the necks straight. One, an old .284 Win. seating die from the junk bin, is merely a threaded collar for holding the expander plug that I cobbled up from die 'parts' and added the tapered expander plug that I turned ont eh little lathe I have.
This plug enlarges cases from .25 cal. up, to .42" cal. in one pass. The expander plug sticks 1/2 way out the bottom of the die, thus the case to be expanded merely is run up over the plug then retracted. The inner size, ie: .284 necking does not effect the case expansion. The die body is only used to hold the expander button.

Using this die, I have expanded .25/06 brass straight in one pass with no looses on once fired cases.

I use Imperial die wax or Ponsness Warren's STOS as the inside neck lubing for the expanding process.

The die body on the left is a .44 mag. expander die body, with an angle ground on the bottom of a .458 expander die plug so it will enter 8mm or larger case mouths. It expands them to .45 cal. in one pass.

I could have used the .458 (or .45/70) expander die body but didn't as I had the expander die body in the junk bin as well as the expander plug purchased as parts at a gun show. "Parts" like that are very handy to have around, so I usually pick them up is well priced.

A .44 mag. expander will also work if ground on the bottom to enter the smaller case mouths.