if it works for you then go for it. I don't use ballistics programs either. I prefer to shoot my rifles at all the required ranges from 8-55yards for FT and 8-45 for HFT. I tend to go for yard increments where it's really critical. Two yards where it's not so critical and five for the rest. Your way would be too simplistic for my liking particularly when I may encounter really small reducers when really accurate aim points are necessary.