Re: Necking up 6.5-284 brass
if you use a normal sizing die you will need a tapered ball or expander button on your decapping pin. They are usually carbide and can be done very easy. Or you can get an expander die and the 7mm expander to do it, either way works well. If you were turning brass then go the second option as you will need to expand then use a slightly smaller mandrel for turning.
One issue you may have is if your chamber was cut for the standard 284 and you use Norma or Lapau brass it may not work well, with clicking when lifting the bolt handle even with light loads. I had this happen to me when I had a LR 6.5x284, it was cut w/ the standard reamer and tried to use Lapau brass. As soon as I switch to Winchester brass no more issues.