I am guessing it will hit lower. Simple Physics would suggest such a thing. How much lower is the question. A lot will depend on the bullet design. If the 240 grain for instance is a T/C Cheapshot and the 300 grain is a Hornady .45 caliber SST then there might not be that great of difference. You will also need to shoot the rifle to see if they perhaps fly to one side or the other of where you want them to hit. A good example is I was shooting T/C Shockwaves out of the Black Diamond and getting excellent bullseye hits at 50 yards. When I took 370 grain T/C Maxi Balls at the same range with the same charge, I figured there would be a real difference in where they would hit. I was surprised when they hit only an inch lower and in a very tight group. You are just going to have to go to the range and enjoy yourself with another day of shooting.... should be a law against that.