Not all bullets are created the same nor are they always used the way they were designed to be used . There are people out there that have tons of engineering degrees and aeronautical degrees that have set to work on bullet designs and can tell you in great detail about the design and the intended use the why this is that way or that makes a bullet react in a certain manner at this point and then this way down range at another point . I have found that if I start with a rifle that has this twist rate it was designed for a weight range of bullets so then that is my starting point bullet weight . Next I look at what I'm wanting to do with that bullet , hunt , target shoot . So then I look at the bullets offered by the different manufactures for my intended use . Different bullet manufactures will use differing materials for bullet construction , copper alloys in the jackets , different lead alloys for the core or lead free designs . Some bullets are designed for good flight abilities but don't open up very well , target bullets , and full metal jacket bullets , still others are designed to nearly explode but fly well small hunting and small animal bullets . Some bullets are designed to be used at speeds in a certain range due to their design , jacket thickness , hollow point design , or spire point design , core metal and it's density toughness or brittleness . Some bullets have a boat tail design while others have a flat base and others may have a modified boat tail base with a step in it , some have copper base's and others exposed lead . Some bullets are designed to wound , military use mostly , some are designed to have massive tissue damage , self defense rounds , and some are designed to kill an animal quickly with little to no exit and destroyed meat . This is a very complex subject and not an easy one to figure out in a short amount of time but for those of us that are inclined to do so there is a ton of information out there some that you need to have an IQ of at least 145 or more to understand and still other study material that most of us can understand . For the vast majority of us like me I just look at what the manufacture advises they be used for .