According to TOW, there's roughly 0.45 lb. difference in the 7/8" versions between .45 and .50, so I expect the difference will be the same with 15/16". That would make the 15/16x42 .45 cal weight about 6.61 lbs vs 6.16 for the .50. For me, it doesn't seem like enough difference to get worked up over (could even be a good thing), but some people don't like weight up front to start with.