I was wondering if I could neck size this and run it through my Redding body die that is already set to -.003 to my chamber fired brass. Or should I full length size it to fire form it, and then neck and body size it after the first firing.
If the brass will already fit the chamber, I would simply neck size, load, and fire it. This should achieve a fireforming cycle and any case resizing should be based on that set of measurements. IMHO it's best to limit brass working to reduce work hardening.
When I rebarreled my rifle I had a lot of brass from the old barrel that I though would just "fit" the new barrel chamber. Even test fit a few pieces. Those pieces seemed fine so I loaded a bunch of brass that had been fired in the old barrel. Big mistake. Even though the first couple of pieces of brass fit, I had a whole bunch of loaded rounds that didn't. Couldn't close the bolt on them and ended up running them through a Body die in order to use them
To the OP, since the brass is once fired, I'd go ahead and use the body die that's adjusted to your rifle's needs and then neck size separately. This will assure you that all your rounds will fit. There's nothing worse than trying to remove a round you can't close the bolt on, but is stick firm enough you have to use a brass punch on the bolt handle to remove it (Thank you PTG for making a nice stout one-piece bolt).
A little extra working of the brass is minor compared to the frustration and potential dangers of trying to remove a live, stuck, round.
Actually, I think Deadshot's advice is an excellent alternative approach.
For my part, I don't anneal, so it's probably more important in my regimen to minimize brass working. I also tend to keep my loads more on the moderate size to limit case stretching.
Incidentally, I have found a paint can opener hook that doubles pretty well as an emergency bolt action extractor when the main extractor is failing. The only time I have had a need for it was when shooting in the wet and having wet ammo in the chamber resulting in a blown primer, which took out the extractor.
Thanks guys one more question, does neck sizing "stretch" the brass at all. I ask because should I neck size first and then bump the shoulders or does the order of sizing not matter.
What stretches brass is the act of firing in a chamber with too much clearance.
As far as neck sizing / body die sizing, if your body die sizes tight enough at the base, it should work. Mine does not. With a Redding +.006" shell holder, it sizes the base for zero clearance. After 3-4 firings I need a small base die. So if the brass you have has been fired in a NATO chamber, and your chamber is tight like mine, you may need a small base die.