Sounds like you've answered your own question.
I would have recommended an LBT WLN 300 grain gas check sized appropriately for your gun's cylinder throats. My "luck" with them on deer shows they kill as well as 240 grain JHPs without the meat destruction. If you wanted less weight, I'd have said WFN ... I believe 300 grains is the lights you can get in the long nose version. I would go ahead and spend the extra $50 or so for a 4-cavity over 2-cavity mold.
Tom
