The difference between 9mm and 45 cal.?

The answer is not as simple as you would like it to be.

Firstly, they are not roughly the same size. A .45 caliber is quite a bit bigger around than a 9mm. However, the diameter of a bullet is only one component of the overall ballistics characteristics. Other components include the weight of the bullet, the bullet configuration, the powder charge used, and the length of the barrel from which it is fired.

Let’s talk weight first. In general the .45 cal is a bigger bullet and thus is heaver. This generally means a projectile that will loose its energy (slow down) quicker. However, being heavier also means more ft/lbs of energy delivered at the impact site than a lighter projectile traveling at the same speed.

Ok, now lets talk bullet configuration. There are many different ways a bullet can be put together ranging from a hollow point, to a fragmentary round like a “glaser” to a fully jacketed “hard ball”. All of these different configurations behave differently upon impact. A hollow point round is designed to mushroom, which causes it to loose all of it’s energy relatively quickly on impact. The result is that shortly after penetration all of those ft/lbs of energy are more rapidly dissipated into the target. Contrast that with a fully jacketed round that is designed to hold its shape better and will simply poke a nice clean hole.

Next you must consider power charge. It takes a bigger charge to fling a bigger bullet. The .45 has a larger diameter so can accommodate more powder. However, it is easier to fling a smaller bullet like a .9mm faster. There is also bullet weight to consider. Just because a bullet is bigger around does not mean that it is heaver. So, it is a balancing act between charge, diameter, and bullet weight regardless of what caliber you are using.

This web page seems to make a sincere attempt to compare the two on what is apparently a hotly debated topic:

Conclusion and Thoughts on 9mm vs. 45ACP:

-It is my belief based on data from serious researchers that with FMJ, the 45-caliber automatic is more potent than the 9mm. That does not mean that I believe either to be anywhere near the top of the list for self-protection. I do not believe that “they all fall to hardball.”
-I do tend to agree that the expanding defensive bullet should penetrate between about 12 and 14”. This may be more than required for a straight on, unobstructed chest shot, but it better insures punching the vitals should an intermediate target like an arm get in the way. It would also likely be more effective if the shot was made from the side rather than the front or back.
-I am convinced that the size of the wound channel from an expanded .45 ACP bullet will be larger than that from the 9mm and this should make it more effective, but I have not seen a noticeable difference on animals as mentioned previously. I am equally convinced that gelatin results may or very well may not match what actually occurs in flesh-and-bone targets.
-Probably the most important factor in stopping power (regardless of caliber) remains placement. That this can be difficult to obtain in the life-and-death fight scenario doesn’t change the necessity for it if we want the opponent to go down for physical rather than psychological reasons.
-With the best loads, I opine that .45 ACP is a better “man stopper” than 9mm with its best loads, but am not sure of by what margin.
-I do not believe that a 9mm loaded with the better loads is an inadequate defense gun and frequently tote one myself.
-I do not “trust” either the .45 ACP or the 9mm (or any other handgun caliber) to provide the elusive “one shot stop” unless the brain or central nervous system is destroyed.
-I am not convinced that the temporary cavity produced by handgun bullets is totally irrelevant, but I also have no idea of how it may actually contribute. I wish there would be more serious research in this area.
-Either of these calibers with any load may fail to provide the desired results even with a “good” hit. Either may require multiple “good” hits.
-Perhaps either caliber would provide fewer failures if we practiced as much as we worry about our caliber’s stopping potential.

Both answers above are correct and have merit. our police department issues Glock 40 to its officers as the main weapon of choice. the Glock 40 has almost the knockdown power of a .45, but does not have the same recoil. the Glock 40 is a terrific and accurate weapon. i have scored 100 many times at our gun range with this weapon.

Great answers all, thanx

I read where a lot of people in the army complain about the 9mm in the Beretta M-9 having unsatisfactory stopping power. They by law have to use FMJ which is really a target range projectile. Stupid Geneva convention. Many would rather they go back to the old war horse 1911 .45 cal ACP. Fewer shots can be loaded at a time but the idea is each one is the shit.

Actually, I believe that would be the Hague convention…and since when does the U.S. actually follow it?

I went with 9mm reasoning that it was the smallest caliber one can probably go with while still being able to stop an assailant with two shots. Of course, I’m not limited from using hollow points.

ACP is autoloading colt pistol?

FWIW, I believe that the .40 SW is a nice compromise between size (that would be overall size of the firearm, not diameter of the round) and stopping power.

@incendiary_dan When does the US follow the Hague? probably 100% more than our enemies do, which is never. In trying to fight an impossible war the 1st world countries have rules to follow that nobody else need know about. So a lieutenant that loads his mags with 9mm Corbon hollow point rounds and is discovered doing that will likely end up in Leavenworth due to war crimes.That is wrong.