Making 260 brass
Here's the deal with making 260 brass.
1)Remington makes staright out R-P brass in .260 Rem. Thats one way to be had. Remington has improved somewhat over the years on there brass quality.
2)Necking down .308 brass..Depending on your brass, Especially Lapua, when you neck down to .264 dia. You will get a build up of brass around the neck junction and usually results in neck-turning. However with other brass, Winchester, BHA, etc... they are thinner and may not require turning and that will all be determined upon your chamber specs..necking down 7-08 also follows this rule to.
3)Necking Up .243 brass. (IMHO is the best way to form good quaity 260 or 260 Improved versions) This method requires no neck turning. Just run the .243 brass into your .260 FL die w/some imperial wax and should form fine. You will get that final finished product after its fired (quote"fire formed"). I then would simply use a Lee 260 Collet die to just resize the fired case (fired case will measeure around .266-.267) and the Lee Collet die will JUST Resize the neck back to .263, just enough to get a firm grab on the bullet. No need to bump the shoulders back or FL again. You may get away using the Lee die like this for 4-5 shots before bumping the shoulder back.
I hope this helps..