Bullet Weight vs. Velocity – striking the right balance is important

Published by the LearnAboutGuns.com Author on September 14, 2008 at 12:39 am
LearnAboutGuns.com > How-To Guides and Other Info > Bullet Weight vs. Velocity – striking the right balance is important

A rather contentious issue in the area of self defense is that of proper bullet weight/velocity – I would guess that this is second only to the “which caliber” or “which gun” question.  On one side is the idea that a lighter weight but faster moving bullet is superior, while others contend that a slower moving but heaver bullet is the better option.  This article addresses my thoughts on the issue:

Why bullet weight/velocity trade off occurs
First a quick and simple primer on the physics involved: Firearms burn gun powder to accelerate projectile(s) down the barrel and on toward the target.  The amount of gun powder that can be placed in a given cartridge is limited, primarily by what the gun can handle without experiencing a catastrophic failure due to excessive pressure as the powder burns.  This means that the propulsive force is limited, and the primary factors for bullet performance become bullet weight and bullet speed.  Physics demands that a reduction in bullet weight will result in that bullet being accelerated to higher speeds, while an increase in bullet weight will result in that bullet being accelerated to lower speeds.  In sum, you can either have a bullet that is heaver but slower, or lighter but faster.  Finally, a bullet that travels faster will fall a shorter distance toward the ground on its way to its target, making aiming a bit easier at longer ranges.

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The case for a lighter weight but faster bullet
Those who advocate for a lighter but faster bullet will point to the fact that the formula for kinetic energy is 0.5mv^2 (1/2 of the mass x the square of the velocity); meaning that a lighter bullet at a higher speed will carry more kinetic energy than a heavier bullet at lower speeds.  Some will argue that “hydrostatic shock” or “energy transfer” from a high speed bullet will incapacitate the target, independent of the tissue and organs actually struck by the bullet – however this argument seems to lack any basis in fact, at least at the speeds reached by handguns, shotguns, and many rifles.  Another argument in favor of a lighter but faster bullet is the likelihood of more effective and reliable performance of a hollow point bullet when it is traveling faster – this is because a hollow point bullet that is moving too slowly may not reliably expand.  Finally, a lighter bullet can offer reduced recoil without sacrificing kinetic energy levels, which can matter for those physically unable or unwilling to tolerate much recoil.

The case for a heavier but slower bullet
Those who advocate for heavier but slower bullets will argue that bullets work for self defense by penetrating the attacker’s body and physically disrupting vital organs and tissues, not by transferring kinetic energy.  They will also point out that a bullet that is way too light can fail to penetrate deeply enough to reach vital organs, making that bullet unable to stop an attacker.  Finally, advocates of heavier & slower bullets will say that modern hollow points reliably expand at a wide range of velocities, including lower speeds.

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My Opinion
I prefer bullets that are slightly lighter than normal, traveling at a slightly faster than normal speed, and believe that this combination will offer the best overall performance.  Note that I say “slightly” lighter and “slightly” faster, as when taken to extremes, a very fast but very light bullet is not very effective, just as a very heavy and very slow bullet is not very effective.  In the self defense scenario, a bullet’s job is to penetrate the attacker and disrupt vital organs in order to stop the attacker from continuing their attack.  A slightly lighter bullet will provide the required penetration, and help ensure good expansion of hollow point bullets, while at the same time providing less recoil (which helps allow accurate follow-up shots).

An example of what I find to be the ideal trade off between velocity and weight
In my favorite pistol caliber, .40 S&W, I prefer a 140 grain homogeneous copper hollow point bullet driven to about 1200 – 1300 feet per second (depending upon barrel length), as offered by Cor-Bon.  Weighing in at 140 grains, this bullet is on the lighter side of most .40 S&W offerings, but will reliably penetrate more than 10 inches of ballistic gel.  Recoil is softer than 155 or 165 grain rounds, the bullet retains about 100% of its weight, and reliably expands to .64 caliber while penetrating to about 12 inches.

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As with my artiles addressing “which caliber for self defense” or “which gun for home defense“, I’m sure that opinions here will vary :)

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  • http://10-lbs-to-lose.blogspot.com TKA

    Interesting. I had no idea that any of this mattered. I always figured that if it could come out of a gun and fly through the air, it'll kill you.

    • georgesteele

      You are absolutely, positively correct – which is why you never point a gun at anything you do not intend to kill immediately. A .22 BB cap is lethal, as is a .458 magnum elephant round. There are 2 practical caveats, however, which bear on the issue of which you would choose if you are carrying a gun for self defense: shot placement and incapacitation speed.

      A .22 bullet that hits you in the big toe, or grazes an ear lobe, might not kill you unless you die from a wound infection; if it hits you in the brain through an eye socket, you will likely die much faster. That’s the shot placement issue, which bears on whether or not it makes sense with your body weight, hand strength, eyesight, coordination, and practice frequency to count on precise placement and a low recoil firearm, or go with a heavier recoil gun that is more lethal but may be more difficult for you to control and fire accurately. Again, these issues bear on the lethality of the weapon/shooter in combination – i.e., will you kill your foe.

      Then there is the incapacitation issue, which is wholly different. The object of incapacitation is to stop your foe immediately and decisively, denying that foe the opportunity to retaliate against you and cause you harm – “drop him in his tracks”, as it were. You won’t accomplish this if you hit an attacker in the big toe with a .22. You may not accomplish this if you hit an attacker in the heart with a .45.

      A read of the literature shows that impact analysis of bullet effectiveness typically dwells on the “size of the wound channel” – width and depth. Width because a larger opening means more profuse bleeding, all else equal, and depth because the more body mass traversed, the higher the likelihood of greater organ damage. Both bear on the lethality of the wound – whether or not it ultimately kills the target. Neither bears directly on the incapacitation of the foe – the immediacy of the effect of the bullet.

      Immediate incapacitation usually requires either immobilization through destruction of a locomotor skeletal element – a broken femur, for example – or a direct central nervous system (CNS) impact – spinal or brain impact. Most people who are defending themselves want immediate immobilization of the foe – in many cases, with no concern for the lethality of the effect. That is, if he lives, fine – as long as I get away unscathed.

      Immobilization tools like Tasers and Mace are aimed at this latter objective, and focus on CNS attack – direct (Taser) or indirect (Mace) – rather than lethal disruption of organ function. This needs to be factored into your choice of weapon – what are you trying to accomplish? Hunter – lethality; defense – immobilization. It is extremely hard, even with a very powerful handgun, to immobilize a foe instantly. And firearms in general, sending heavy, hard objects at very high speed through flesh, have a distinct problem with collateral damage potential from overpenetration.

      No strong evidence exists that at typical handgun velocities, even with large caliber, reliably expanding hollow point bullets, there exists a “hydrostatic shock” effect that immediately incapacitates a foe, even when a single bullet adequately penetrates a body’s center mass. But you are more likely to achieve incapacitation with such a high velocity, expanding hollowpoint bullet if it is accurately placed by being fired from a controllable gun with which you have adequately practiced defensive shooting. That means affordable ammunition that does not punish you with recoil sufficient to dissuade you from adequate practice.

      And that’s the tradeoff – against a non-lethal incapacitator like a Taser or Mace/pepper spray, if either is legally permitted in your jurisdiction.

      Side note: E=MC^2 – Einstein, mass-relativistic energy conversion equation; E=(1/2)*MV^2 – Newton, kinetic energy – dynamics of a moving body in space. C is the speed of light constant in Einstein’s equation; V is the variable Velocity. They are related in form only, not meaning.

  • lolz

    Then howcome einstein's formula for energy, E=MC^2 implies that the heavier bullet, the more energy it has, regardless of speed?

    • http://www.learnaboutguns.com The LearnAboutGuns.com Author

      E=MC^2 only comes into play when converting matter to energy, or vice versa (e.g. when nuclear fusion or nuclear fission occurs). Unless atoms are being split or fused (as takes place in a nuclear bomb, nuclear reactor, or the sun) E=MC^2 is inapplicable.

      • Prof Emmit Brown

        You are correct, forget other post .. it is the mass – energy conversion equation , at the atomic level . It is the equation scientists used for approximating the nuclear yield of an atomic fission device when developing the Atom bomb.

    • hicus

      That's like saying the sun comes up because there is water in the ocean. Don't quit your day job.

    • POTUS

      No, energy (E) is DIRECTLY related to both mass (M) AND the square of the CONSTANT, speed of light (C). Thanks for playing, though.

      • Adam Hampton Jr.

        You are messing up Energy and KINETIC Energy here. Thanks for playing, too.

  • Robert Hulton

    me and my dad have a bet on what the gr means ob a box of rounds for example a 9mm gr weight is 115 gr is that the whole cartridge or is it just the porjectile

    • http://www.learnaboutguns.com LearnAboutGuns.com

      The weight refers only to the projectile.

  • Lloyd Booth

    The US Army had tested the .45 caliber with the 230 grain bullet many years ago. The findings indicated the .45 caliber with the 230 grain bullet was the match-up to effectively incapacitate an enemy attacker. The tests conducted shot up every thing from animals to cadavers to gelatin. Those tests are good enough for me. I carry a .45 Hi-Point with a 45 Super, 230 grain. Bullet resistant vest or full suit, I am confident the attacker will fall on the first shot, well placed or not.

    • Jonathan Phillips

      The US Army was restricted to FMJ ammunition. In non-expanding bullets, heavy weight always wins. Rather than leave it at that, let me explain: In FMJ bullets, damage is done through direct organ damage and blood loss. A lighter bullet (caliber remaining equal) will tend to penetrate less, as its lower mass leads it to carry less momentum through a medium; thus the heaviest bullet will tend to leave the longest path through a medium (in this case, an enemy). When there is no expansion to rely on, a nice long track increases chances of a vital organ being hit and causes a proportionate increase in internal trauma (admittedly, no where near the trauma a proper expanding round would cause, but military ammunition cannot expand or fragment, as it is against the Hague Convention of 1899).

      Oh, it was also found that a heavier bullet decreased chances and severity of a deflection or ricochet, which the FMJ bullet is prone to (at least when compared to other bullet designs).

      All this is to tell you the following: The army was using a 230 grain FMJ bullet because THEY HAD TO. For self defense situations, it is SEVERELY inferior to modern expanding bullets. Not only is it inferior, it is pretty much irresponsible unless your country/state/municipality forbids use of hollow point ammunition (which a few actually); in those situations they have Expanding FMJ's that are usually legal, though I'd check with local laws prior to purchase.

      FMJ's have serious overpenetration issues when used in a defensive situation, leading to possible collateral damage (or worse, hitting an innocent through a wall or attacker). Missed bullets are much more likely to deflect/ricochet off of hard surfaces. They are much less likely to stop an attacker, as internal temporary and permanent stretch cavities are much smaller (in the case of a temporary stretch cavity, basically its non existent with FMJ's, which means the initial "shock" of the hit is massively reduced). The only benefit an FMJ bullet would have in a defensive situation would be if you had to shoot through an intermediate barrier, such as a car door, heavy door, light walls, etc. and modern bonded or solid metal hollow points have greatly increased the ability of a hollow point to maintain its shape and expansion ability while passing through such barriers, so that argument is basically moot. For the love of God, use proper defensive ammunition.

      I first thought you meant that 230 gr hollow points were your ammunition of choice, but then you stated the army trials . . . basically you state that you carry a 230 gr FMJ because an army test that (at the time of this writing) is 101 years old . . . and that they were using to find the most effective form of an ineffective bullet design due to the restrictions of a prior military agreement. . . pretty poor choice there, bud.

      • Bud

        I forgot about the experts who comment in these forums. You’re forgiven for bashing my choice of caliber based on your lack of data. Attackers may wear bullet resistant vests, and many in security have confidence the .45 Super 230 grain JHP will suite an encounter just fine. Some security officers alternate load magazines FMJ/JHP/FMJ, since the environment of attacks are the choosing of the attackers.

        • John

          Totally right, an attacker might wear a bullet-resistant vest. In that scenario, you're better off with a rifle than a handgun because your 230gr FMJ .45 ACP will never penetrate kevlar. And the reason some security officers alternate loads is for feeding, not for anti-armor capabilities. You use steel-core ammo to break body armor.

      • Fire in the hole

        I'll bet anything I shoot at with the .45 FMJ will go down for the final count, man or beast.

        • hicus

          BE sure you have the funds to cover your bet because you will lose.

      • hicus

        Who cares what the military comes up with. I am a civilian living in a civilian environment. I have to be concerned with collateral damage..In a civilian environment there is jail time and law suits. Attacks are close up and fast and many times there are other people around. The safest round is a .410 load of # 4 in the face.. It will deter the attacker 100 percent of the time and limit collateral damage. Collateral damage may not hurt you physically but it can ruin your life forever.