As most of us know. The energy of a bullet in flight is an equation of velocity and mass. The more energy the bullet has, the harder it is to stop and in theory will do more damage to its intended target. Thus a 230 grain bullet traveling slower then a 115 grain bullet can have more energy and thus in theory create more damage. However, I ask, wouldn’t the cross section diameter otherwise known as caliber of the bullet also have an impact on damage on a target. Example being two 185 grain bullets traveling at the same speed, with one bullet being 9mm and the other being 45 caliber. Wouldn’t the 45 caliber do more damage due to its cross sectional diameter being larger? Yes the 45 caliber bullet would be shorter and the 9mm longer, but the 45 caliber should produce a larger hole? Correct? (Yes, 185 grain 9mm bullets are rare, to non-existent, but this is just an example for discussion on damage theory) Thus the reason we have hollow points and other various types of bullets that use expansion techniques to increase their cross sectional diameter either in flight, or upon impact with the target. Thus if we were to invent/discover a damage equation, it would have to include not just the bullets weight and speed, but it’s cross sectional diameter? Correct? Does a damage equation even exist? Example again which would cause more damage, (assume FMJ-RN) a 9mm bullet with energy of 300 foot/lbs or a 45 caliber bullet with 250 foot/lbs? Yes the 9mm has more energy, but it’s also a physically smaller bullet then a 45 caliber bullet. How many foot/lb difference of energy would be needed to make the smaller 9mm create more damage? (Yes, I realize the energy example may not be realistic energy amounts for said caliber but this is just an example for purposes of discussion) IMHO Damage to the intended target is an important consideration when choosing caliber and ammunition be it for hunting, or even self defense against animals, or humans, and the location we are wanting to use our firearm and ammunition. Ie, in many instances, we want to reduce any potential for collateral damage. The other question I ask to everyone, is how important is your consideration of damage to your target do you consider when choosing a caliber and ammunition for said caliber?