Why don't you find a place where you can shoot out to 300 yards and find out what your rifle does? If you shoot the rifle at long range, record the pertinent data like temperature humidity, elevation, wind etc, you can make up your own drop table for each load. This data will be rifle and load specific and will be much more accurate than computer generated guess work. If you can't find a place to shoot out to 300 yards, it doesn't seem that you'll need to know the drop at 300.