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Wikipedia has a solid article on nose cone shape: https://en.wikipedia.org/wiki/Nose_cone_design. Here, we're going to focus on how nose cones are typically applied in rocketry as we use it. As we start to make our own nose cones, we will update this. Typically, we buy Ogive nose cones because they are easily commercially available. The length to diameter ratio is usually 3-6. See the familiar vendors page for places to buy nose cones.
In addition to drag reduction, nose cones are particularly useful for storing ballast, payloads, and/or even avionics components.