I have shot the 6.5 WSM ( known as the 6.5 Badcat to some

) for about six years now, and also shoot the 6.5WSSM.
The cartridge is a pretty cool number.
Old Badger and I originally used 300WSM brass, but when the 270 WSM brass became available , we used that , as there is less neck turning involved.
As far as bullets go, I have shot animals with Barnes XLC's and Sierra Game Kings in the 140 grain weights.
I have used about 6 different bullets in it all the way out to 1k, and the 140 Game King works very well , as far as Accuracy and such, but
140 Alberta Wildcats work stupendously also!
Richard builds a fantastic bullet in the 142 range, and can build them with a very stiff hunting jacket.
I received some heavy 165 grain rebated boatail ULD's from hin recently that I can't wait to try out iin my son's 6.5/284 and the 6.5WSM.
You should give him a call if you are interested.
The Barnes TSX works well also in the accuracy tests I did at 200 yards.
BTW, Higginson's has the 6.5WSM dies as a stock item for far less than RCBS and they work very well!
Cat