Originally Posted by winmagman
270 and 300 wsm brass have the same dimensions (except neck diameter obviously) so the 270 would be easier to use. Probably the simplest route to go would be to pick up a set of Redding 270 wsm "S" type bushing dies and switch out the 270 bushing for the size needed to get the desired neck tension on your 6.5 wsm.
I agree here, I use 270WSM brass for my 6.5WSM. An S-Type die is the only way to go IMHO. As far as bushing selection goes, you are between a rock & a hard spot. The best way i've come up with to select the correct bushing size is to have a loaded round to measure (from your own lot of brass/bullet). I can give you some sizes to start with if that'll help, but you may end up buying more than one bushing to get the size just right. Do you plan to neck turn or are you running a no turn chamber? (I am).
Also, I would recommend you buy the FL S-Type die. Meaning full length sizing, bushing style.