I realize this thread is ancient, but what process did you use to resize the 300 RUM into 375 RUM? Were there any "gotchas", or special prep you had to do? Or, did you just lube the 300 RUM cases and ram them through a 375 RUM full length resizing die? I've contemplated getting a 338 RUM expander ball and running that first, but if that is not needed I don't want the extra steps.You can easily make 375 RUM from 300 RUM brass. I have made quite a bit of it from 300 rum brass when 375 is hard to find. It turns out just a touch shorter but works just fine.