My Cooper 6.5-284 uses Nosler (reported to be made by Norma) and Lapua brass without neck turning, but the best accuracy is .284 Winchester necked down. I found Lapua brass a bit heavy and harder than the Nosler, I'm not really a fan of Lapua brass due to oddball issues with distorted primer pockets and an unidentified problem where it wont rechamber in the same rifle that all the others work normally in. My friend has the same problem with Lapua brass, we are left scratching our heads.
I remembered reading an article about the 6.5-284 and neck thicknesses, here it is in case you haven't seen it:
http://www.accurateshooter.com/cartridge-guides/65x284/ Scroll down to the Preferred Neck Diameter section.
Good luck.