Question about bullet calibers and hitting power

I had always thought that the bigger the bullet, the more ‘punch’ the bullet packed. But I’ve heard that 9mm rounds often aren’t as powerful as say, .38 or .45 caliber bullets. Now I don’t have a ruler handy, so I don’t know if the latter are actually as big/if not bigger than 9mm but I haven’t heard of metric rounds bigger than 9mm. I believe NATO rounds are only 7.62mm which is even smaller than that.

Does the diameter of the bullet have any bearing on the power? Someone made a chart on SDMB that listed the force of several different guns, and it seemed that the medium-sized calibers were the most powerful. But what about things like the .50 caliber rifle? I saw an article on the news about these guns (the feds wanted to ban them, if they haven’t by now) and they were capable of blasting a coffe-can sized hole in a brick wall or hitting a target from a *kilometer * away!

9mm is equivalent to a .35, therefore smaller than a .38. There are 10mm bullets, and probably other large metric sizes as well.

The size of the bullet is only one factor in its power. The amount of powder in the casing also has a big impact. More powder = faster bullet = more power. Thats what “magnum” means: it’s the same size bullet with a longer case containing more powder.

Thats what I figured. I always noted that rifle cartriges often had like 4/5 of their length a powder charge. When I was younger I was quite surprised that the bullet was much smaller than the cartrige it was in.

Any benefit to having the bullets have blunt tips? Why not make them as pointy as possible?

bullet weight and speed are what determines the ‘punch’. A small diameter bullet at high speed can have many times the amount of impact power as a wide diameter bullet moving slow.

Generalization: A pointy tip bullet can just zip right through a target (or armor). A blunt, or hollow tipped bullet will mushroom or split up inside the target, causing massive tissue damage. In combat, or hunting, you want your first shot to drop or incapacitate the target.

Blunt tips, or hollow points, are good for shorter ranges where aerodynamic efficency is not as important. All other things being equal, and they probably aren’t, a projectile with a blunt tip will slow down (lose energy) faster than one with a more aerodynamic shape. Most rifle cartridges generally are loaded with “pointy” bullets as they are intended for long range shooting.

Exceptions are cartridges loaded for rifles with tubular magazines. These would include cartridges like the 30-30.

A bit of math, kinetic energy is related to the mass of the object but the square of the object’s speed.

Therefore, if you double the mass of a moving bullet, you will double the energy on impact but if you double the speed of the (original) moving bullet, you’ll quadruple the energy on impact.

Faster is better than heavier.

I had a college professor who was working on rail guns. He claimed he could blast a pencil-eraser-sized piece of light plastic through a roughly inch-thick sheet of steel with a 13-inch rail gun. Not a whole lot of “M” but bucket-loads of “V”.


Note: the M-16 (Nato style) comes standard with 5.56MM.
The 7.62MM you’re thinking of is Eastern Bloc style, and often seen in the AK-47.

.38 caliber is a bit of a misnomer. Bullets for .38 special and .357 magnum are only one or two thousands bigger than a nominal .354-.355" 9mm bullet. The mixup comes from the old Colt .38 which used a heeled bullet similar to a .22 long rifle rimfire. The outside diameter of the bullet was the same diameter as the case. When the switch was made to internally lubricated bullets that fit inside the case the 38 designation was retained though the bullet and barrel diameter were now nominally .357" in diameter.

This misnaming is common in firearms for various reasons. The .38-40 cartridge was misnamed the opposite way. It’s actually .401" diameter making it virtually identical to the modern .40 S&W and 10mm calibers. 44 caliber cartridges are typically .427-429" in diameter while Colt .44 caliber cap and ball revolvers are the same as typicsl .45s.

Aside from the .38 Colt the only “true” .38 I know of is the .38-55 used in some lever action and single shot rifles.

Mr. Woodall - The ComBloc round you refer to is the 7.62 X 39. There is a round known as the 7.62 NATO; it is 7.62 also, and is called .308 Winchester here in the U.S.

Isn’t a .25 caliber considered to have much less “punch” than than a .22?

No simple way to answer that. You can’t change any one factor in the ballistics of a bullet without effecting the others. A .25 caliber rifle bullet with the same mass as a .22 caliber bullet will have a worse ballistic coefficient and more drag so less velocity downrage given the same muzzle velocity.

Terminal ballistics or “punch” as you put it is a very complex thing. It boils down to having a bullet designed and constructed to put as much of its kinetic energy as possible into the target. Two biggest factors are what’s the target and how much velocity? Are you trying to punch a hole in steel armor, push a steel plate “knockdown” target in competition or quickly and humanely kill a game animal? What works best in any of those situations might perform poorly or be disasterous in the others.

People have been arguing about this for hundreds of years. Much of it comes down to personal opinion.

Here’s my opinion, for what it’s worth: When it comes to “knock down power,” bullet size is much more important than bullet speed and/or kinetic energy. This is because a larger bullet has a better chance of damaging vital organs and blood vessels (simply because it’s bigger). Those who profess kinetic energy is the most important factor often talk about “energy dumping” and “hydrostatic shock,” both of which are insignificant or non-existant IMO.

As stated in below posts, the “punch” depends on both the velocity and mass. Velocity is exponential in it’s effect on energy delivery to a target but also decays exponentially (aerodynamic drag) over distance. Punch against a hardened target such as armor plate is pretty much a function of mass and velocity. When you add a human or animal to the equation, other factor also weigh in. What is usually discussed is how quickly the bullet gives up it’s energy to the target. Deformation of the bullet is important - you don’t want it to fracture or crush immediately on striking [no penetration] nor do you want it to remain intact and pass through the target without giving up much of it’s energy. The shape of the bullet tip, composition of the bullet, use of a false (aerodynamic) windshield all come in to play. The parameters evaluated in target effect include wound depth, size of the temporary wound cavity, and size of the permanent wound channel. Cavity size depends on all the above factors plus mass distribution (bullet balance). If the bullet tumbles on entry it will make a cavity much larger that the caliber/velocity/mass would ordinarily indicate. A tendency to tumble may give too shallow a cavity - not get to an organ; be poor aerodynamically; or not penetrate at all. Where you hit is an overriding concern of course, you need to take out internal organs not simply create a flesh wound. Military experimentation takes place on pig cadavers and in the West, NATO jelly which is kind of a jello mix with the consistency of flesh.

In regard to calibers, the number given is the diameter of the weapon bore, not the bullet which is ordinarilly a few thousands of an inch larger so it “digs into” the rifling twist to impart a rotation. Standard small arms NATO calibers are 5.56mm, 7.62mm, 9mm, and .50cal (12.7mm). Military sizes are usually expressed as a combination of nominal diameter, cartridge case length, and style of cartridge case base. An example is 7.62mm X 39R. This round is approximately 7.62mm in diameter (slightly larger), has a cartridge case length of 39mm and has a rimmed cartridge case head. This is the standard “Soviet” AK-47 round. A common NATO round is the 7.62mm X 54. Same diameter, longer case and rimless design to the head (if rimless, the head designation is usually left off). This round is the NATO machinegun size (M60 or M240 {and other}) and is also used in the sniper rifles M21/24 of that caliber. This was the standard round for the soldier’s M14 in Korea and into Vietnam. Due to differences in cartridge case length and style of head, these rounds, Soviet/NATO, are not interchangeable despite similiar caliber. Commercial designations follow no set standard.

As to the .50cal rifle; the Barret rifle is used by special operations teams as weapon against material, not individuals. The famed Desert Storm hits at 1800meters were against artillery stockpiles, not individual soldiers. The typical round has an armor piercing, incendiary, explosive bullet. Prime targets would be lightly armored vehicles or trucks, ammunition stocks, and dense electronic targets at ranges from point blank to the above 1800meters. Advantages include short engagement times and no minimum arming versus limited penetration/effect against more substantial armor such as a tank where a missile or anti-tank rocket would be more effective.

It may not look it but this was a pretty brief explanation. If you have any detailed questions feel free to ask.

U.S. Department of Justice

Handgun Wounding Factors and Effectiveness

Special Agent UREY W. PATRICK


July 14, 1989

"Physiologically, a determined adversary can be stopped reliably and immediately only by a shot that disrupts the brain or upper spinal cord. Failing a hit to the central nervous system, massive bleeding from holes in the heart or major blood vessels of the torso causing circulatory collapse is the only other way to force incapacitation upon an adversary, and this takes time.

The often referred to “knock-down power” implies the ability of a bullet to move its target. This is nothing more than momentum of the bullet. It is the transfer of momentum that will cause a target to move in response to the blow received. "Isaac Newton proved this to be the case mathematically in the 17th Century, and Benjamin Robins verified it experimentally through the invention and use of the ballistic pendulum to determine muzzle velocity by measurement of the pendulum motion."29

Goddard amply proves the fallacy of “knock-down power” by calculating the heights (and resultant velocities) from which a one pound weight and a ten pound weight must be dropped to equal the momentum of 9mm and .45ACP projectiles at muzzle velocities, respectively. The results are revealing. In order to equal the impact of a 9mm bullet at its muzzle velocity, a one pound weight must be dropped from a height of 5.96 feet, achieving a velocity of 19.6 fps. To equal the impact of a .45ACP bullet, the one pound weight needs a velocity of 27.1 fps and must be dropped from a height of 11.4 feet. A ten pound weight equals the impact of a 9mm bullet when dropped from a height of 0.72 inches (velocity attained is 1.96 fps), and equals the impact of a .45 when dropped from 1.37 inches (achieving a velocity of 2.71 fps).30

A bullet simply cannot knock a man down. If it had the energy to do so, then equal energy would be applied against the shooter and he too would be knocked down. This is simple physics, and has been known for hundreds of years.31 The amount of energy deposited in the body by a bullet is approximately equivalent to being hit with a baseball.32 Tissue damage is the only physical link to incapacitation within the desired time frame, i.e., instantaneously.

The human target can be reliably incapacitated only by disrupting or destroying the brain or upper spinal cord. Absent that, incapacitation is subject to a host of variables, the most important of which are beyond the control of the shooter. Incapacitation becomes an eventual event, not necessarily an immediate one. If the psychological factors which can contribute to incapacitation are present, even a minor wound can be immediately incapacitating. If they are not present, incapacitation can be significantly delayed even with major, unsurvivable wounds.

Further, it appears that many people are predisposed to fall down when shot. This phenomenon is independent of caliber, bullet, or hit location, and is beyond the control of the shooter. It can only be proven in the act, not predicted. It requires only two factors to be effected: a shot and cognition of being shot by the target. Lacking either one, people are not at all predisposed to fall down and don’t. Given this predisposition, the choice of caliber and bullet is essentially irrelevant. People largely fall down when shot, and the apparent predisposition to do so exists with equal force among the good guys as among the bad. The causative factors are most likely psychological in origin. Thousands of books, movies and television shows have educated the general population that when shot, one is supposed to fall down.

The problem, and the reason for seeking a better cartridge for incapacitation, is that individual who is not predisposed to fall down. Or the one who is simply unaware of having been shot by virtue of alcohol, adrenaline, narcotics, or the simple fact that in most cases of grievous injury the body suppresses pain for a period of time. Lacking pain, there may be no physiological effect of being shot that can make one aware of the wound. Thus the real problem: if such an individual is threatening one’s life, how best to compel him to stop by shooting him?

The factors governing incapacitation of the human target are many, and variable. The actual destruction caused by any small arms projectile is too small in magnitude relative to the mass and complexity of the target. If a bullet destroys about 2 ounces of tissue in its passage through the body, that represents 0.07 of one percent of the mass of a 180 pound man. Unless the tissue destroyed is located within the critical areas of the central nervous system, it is physiologically insufficient to force incapacitation upon the unwilling target. It may certainly prove to be lethal, but a body count is no evidence of incapacitation. Probably more people in this country have been killed by .22 rimfires than all other calibers combined, which, based on body count, would compel the use of .22’s for self-defense.

Physiologically, no caliber or bullet is certain to incapacitate any individual unless the brain is hit. Psychologically, some individuals can be incapacitated by minor or small caliber wounds. Those individuals who are stimulated by fear, adrenaline, drugs, alcohol, and/or sheer will and survival determination may not be incapacitated even if mortally wounded.

The will to survive and to fight despite horrific damage to the body is commonplace on the battlefield, and on the street. Barring a hit to the brain, the only way to force incapacitation is to cause sufficient blood loss that the subject can no longer function, and that takes time. Even if the heart is instantly destroyed, there is sufficient oxygen in the brain to support full and complete voluntary action for 10-15 seconds.

Kinetic energy does not wound. Temporary cavity does not wound. The much discussed “shock” of bullet impact is a fable and “knock down” power is a myth. The critical element is penetration. The bullet must pass through the large, blood bearing organs and be of sufficient diameter to promote rapid bleeding. Penetration less than 12 inches is too little, and, in the words of two of the participants in the 1987 Wound Ballistics Workshop, “too little penetration will get you killed.” 42,43 Given desirable and reliable penetration, the only way to increase bullet effectiveness is to increase the severity of the wound by increasing the size of hole made by the bullet. Any bullet which will not penetrate through vital organs from less than optimal angles is not acceptable. Of those that will penetrate, the edge is always with the bigger bullet.44

I believe you’re referring to the 7.62 x 51 cartridge…

Good call Crafter. The 7.62x54mm is the Russian caliber used in the Moisin Nagant bolt action rifles and the semi-auto Dragunov sniper weapon. It’s similar in power to the .30 CAL US/.30-06 and the case has an unusual beveled rim.

Also the M-14 wasn’t adopted until about four years after the Korean war was over. The M1 Garand was still the primary rifle in Korea.

Smithsb: Just wanted to let you know that I feel like a jerk for pointing out a minor technicality in an otherwise excellent post. Didn’t mean to do that, especially to a newbie. (BTW: Welcome to the forum.) Sorry.

<sigh> now I feel like a bully. Sorry to be so nitpicky too.