Same as me. I use 240 grain factory soft points that I buy at the local Allied Hardware. Is it a known/proven/accepted fact that a 300 grain hard-cast cartridge is a better "emergency" stopper? There's more mass for sure, but it'll be going slower. I've never seen those cartridges in the usual stores.
FWIW, if I was really gonna risk my a** while fishing on a beary stretch of river I'm gonna trust my 600 grain Brenneke Black Magic swaged lead slugs. Try to imagine a small oil drum with a stabilizing tail. I've only got 15 ... which should be a lifetime supply