Capt have you necked it down in the past? I’m in the same boat I bought 416 Ruger necked it down to 375 Ruger annealing it and next step to neck down to 300 PRC. That’s the step I’m sketchy on, that’s a big step! Do you use a standard 300 PRC die without the stem or is there a die between? Would love some help before I trash the 375 brass? Also ordered a .308 internal neck reamer. I’ve only necked down 8mm mag to 7 STW which is easy run it through the die and send it!!!
Use a 338 RCM die to go from 375 down to 338, then use the 300 PRC die.