I haven't tried cast bullets in the 375, but I did try them in the 458 and the 416. I think loading standard weights is a good choice, so the sights will still regulate correctly. You can push them close to factory velocities and get good results that way.

Just don't push them too fast. I did that in the Rigby with a 350 grain cast and had terrible leading problems.

But, if you want to shoot NA game, they are the perfect choice.

You don't have to cast your own, as there are several cast manufacturers that make cast bullets in those calibers. Try to find hard cast ones with high velocity lubes on them, then stick to cool buring powders.

RobertD