Ackman
Gold $$ Contributor
I wouldn't be using that stuff, or any filler. I've done literally thousands of Ackley cases working up a load as with the parent case. Then shooting what was an above max book load out in the field on fur. Those fireform loads were actually working load and faster than the parent case with same accuracy as formed brass. A win-win. Have no experience with your 375 or 415, but think cow/any filler is a waste of time and powder and primers.