Just ask John Hoover and family. They use
necked down 284 Winchester brass.
Son Adam shot a 5.044 group, his sister shot 5.906 (she just turned 15),while dad John shot a 6.1xx and mom Diane came in with a
8.6xx. These were all 10 shot groups in the 16 1/2 lb class at Williamsport on 8/16/03.
John Vonieda's World Record 3.151 was shot using necked down 375 H&H Win brass. The caliber of his own design (308V).
Johh Hoover uses not just Winchester brass but the super old (ie not available now) white and yellow box brass. He bought 743 boxes from one guy in Illinois. Good luck trying to find it, but he says the next best is Lapua.