Don't confuse caliber with cartridge. You could wind up trying to equate two highly dissimilar power levels just based on the diameter of the bullet. I see that as a trap - it's entirely too simplistic. One example would be .45ACP, compared to .458 SOCOM. The pistol round starts out at 900 fps, the rifle at 2200 fps, but more importantly, the pistol starts out with at best 600 foot pounds of force, the .458 with over 3,300 foot pounds of force. That means there is a significant difference in the size of the weapon, how you hold it to shoot, your reaction to that recoil, and most importantly, which you choose to match your needed range and target. It should go without saying that one is far more powerful and can handle much larger game and at much further distances. So, no, just because it's ".45" doesn't really mean that much. As a number it encompasses far too much difference in power - if anything the diameter of the bullet becomes relatively useless as a description. It glosses over the more important ballistic factors of how much bullet weight, and how much powder is behind it. This is why the documented results of the old .45 vs 9mm argument keep going on - ballistically they are an effective tradeoff. What the 9mm lacks in bullet weight and diameter it makes up in speed, which is why the lethality of the round using the same style bullets is so similar. What we gained was either a smaller handgun in single stack or the ability to accommodate double stack for the average human hand. The Army had direct experience with it during WWII - we were another 50 years since combat against people who used drugs to increase their tolerance to pain, and the 9mm had performed for just as long in it's role in combat and defense. Using the reports of Germany and the US side by side to analyze the effectiveness of both, it's really no wonder the Army requested a new pistol post war to reflect the technology they had seen work. That is the whole point of the Army Trials of 1954 - even if we didn't adopt the results for another 30 years. We'd done that before, with the .276 Pederson, choosing the existing cartridge in production over making change when it would cost money that wasn't available. Progress comes slowly and not always as we wish. There's a directly comparable field of technology that has delivered the same results, one that uses the combustion of a hydrocarbon compound to propel it's bullet - repeatedly - over 3,500 times a minute. It's the automobile. For those who claim only the larger bullet will do, it's ironic because over the last 45 years we've seen cars drop from 450 cubic inch motors to 3.0 liters - capable of putting out the same horsepower. Yet nobody compares the two in discussions like this.