Re: Neck sizing die
Neck sizing MAY increase accuracy, but not always. It certainly works the brass less, increasing brass life. I like the redding competition bushing style neck dies with the TiN (gold) coating. The busings come in .001" increments, so you can dial up the amount of neck tension you want. For a bolt gun you carefully single load, you probably want the lowest neck tension you can get. The Redding competition set comes with the bushing neck die, a body die for bumping the shoulder back and sizing the body, and a bullet seating die. They feature a spring loaded sliding sleeve that allows the case to engage into the sleeve nicely, before being pushed up into the die to undergo the sizing/seating operation. I believe this is a copy of a Forster design, and I think the Forster ones are cheaper, but just as good.
One drawback to this however, is the body die will not independently bump the shoulder back from body sizing. A bump die would be required to ONLY bump the shoulder back, and leave the rest of the body alone.
In my opinion, a modified FLS die is a good choice. Most FLS dies make the neck way too small on the upstroke of the ram, and then pull the expander ball back through on the ram downstroke to make the neck the appropriate diameter. Essentially, you are reducing neck size .008", only to expand it .005". It is better to reduce neck size .004, and then expand it .001 - or something similar. This works the brass only as much as neccessary, and produces very consistent and reliable results.
My Savage is every bit as accurate using FLS brass as it is with NS only brass.
YMMV