For it to do its work correctly you'd have to have perfect brass. IE all same neck thickness, coencentric thickness, all exact same case length and so on. FWIW IMHO its a crock. I've loaded so many rounds and never crimped(excepting revolver rounds) and never had an accuracy problem. I suspect the issue on the 375 is you have not found its sweet load yet. And with the 300 you have that load, it has nothing to do with the crimp.

Jeff