First you have to know what you are shooting. Then you have to know how close you plan on getting to the victim. If it's a bear, you want to be close range, so you don't need a high powered scope. If you are hunting deer from three hundred yards away, you'll need the best scope you can get. There is no set number depending on what gun you have, it's all about what you are shooting. Since both calibers are very versitile, you might want to get a variable power scope. I have a Winchester 1917 30-06 with a 4X~ 12X that works over a wide range of applications.