I have never used in Winchester 300 WSM brass......strictly norma. BUT....I have some Win. 25 WSSM brass necked up to 6.5 (6.5 WSSM. 264 WSSM, whatever you want to call it) and have beat the living crap out of them. I have 150 pieces that will outlast the tube. I have 7 firings on them now...