I can't be 100 percent sure, but when I was looking at my father in law's Sierra reloading book comparing a .40 180 gr. JHP to a few different grain .45 (180 & up) at max load for both calibers the muzzle energy was not that significantly different, with the .40 being more in some instances. I'm over at school now so I can't verify until this weekend, but if someone else can check it out...