Re: long neck 300 win mag
I'm forming 338 Lapua brass down to 30 cal, but also pushing the shoulder/neck junction back to for the 40 deg shoulder, and a .405" neck length. This is done in the FL die with a .334" nk bushing alone and it works fine.
The only reason I fire form them with cream of wheat instead of seating a bullet and shooting it, is because it has a .335 nk and has to be turned first. COW forming first makes the neck walls perfect before turning/reaming with the K&M tool.
The original neck/shoulder junction is now up in the neck of the new formed case, so necks will be thicker at, and below this point until you do neck turn, so seating a bullet into this area or below might spell chamber clearance trouble, so it should be monitored closely to be safe.
No special dies to form the cases though, and I wouldn't think you'd need any on the 300 WM, a lot less forming on it than the 30/338 Lapua Imp.