Weighty Decisions: Considerations When Choosing a Bullet Weight

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Weighty Decisions: Considerations When Choosing a Bullet Weight

When it comes to choosing which round you want to carry, many people find the choice of different bullet weights perplexing. You may have done all the research necessary to determine the make and model of ammo you feel is best, but even if you’ve settled on that, which bullet weight do you choose? Among the leading hollow points on the market today, there are multiple bullet weights available for each, and often all of them perform very well. There is (as in all aspects of shooting and self-defense) vigorous debate about what is best, though, in reality, the differences are not as significant as some might think. In this article, I will lay out what these differences are and discuss the practical considerations in choosing the bullet weight that is right for you.

Whole Grain Knowledge

I’ve encountered many people who have serious misconceptions about what those numbers, expressed in grains, on a box of ammo mean. A grain is a unit of measurement of mass (for our purposes, weight) in the English/Imperial system. It is 1/7000 of a pound and was originally based on the weight of a single grain of wheat or barley. This unit of measurement is only used in limited areas these days, having been largely replaced with the metric system, but is still the standard unit of weight when dealing with ammunition.

Bullet weights and powder charges are both measured in grains, which sometimes confuses people. I’ve heard some people say that the “grains” listed on the box refers to the powder charge, and the bigger number means the round is more powerful. This is not true, of course. The numbers on the box only refer to the bullet weight. And even so, standard 9mm bullet weights are 115, 124, and 147 grain, though the powder charge generally only weights somewhere around 5 grains. There is no indication on the box of the exact weight of the powder charge, and without knowing precisely what powder is used, that number would not mean much anyway. Powders differ, and it is possible for a lighter weight of one powder to produce more pressure than a heavier weight of another.

The Relationship of Bullet Weight to “Power”

So, is there any truth to the “bigger number = more power” argument, even if it has nothing to do with the powder charge? The answer, unsurprisingly, is “it depends.” If two projectiles are going the same speed, the heavier one will be more powerful, just by fundamental physics. It will have more kinetic energy and more momentum. However, since cartridges are limited to a maximum safe pressure, you can’t make the heavier bullet go as fast as the lighter one. This is the trade-off – heavier bullets mean lower velocity, and vice-versa, all other things being equal.

The primary consideration that “power” depends on is what metric you are using to measure it. Muzzle energy is the most commonly used measurement, which we calculate by multiplying the bullet weight by the square of the velocity. This, of course, puts a serious premium on velocity, as velocity contributes much more to energy (as the squared part of the equation) than the weight does. Even so, with the limitation on pressure, sometimes the medium-to-heavy weight bullets can obtain the maximum muzzle energy, depending on the cartridge and other factors like barrel length. High-velocity, high-energy projectiles are the ones that create dramatic temporary cavitation that we see in gel tests. There is a belief that this apparently explosive energy transfer is “deposited in the target,” causing a damaging shockwave.

However, a lighter bullet will not penetrate as far as a heavier bullet (all other things being equal), as the heavier bullet has greater momentum. Accordingly, some people put the premium on weight over velocity, claiming that the bullet’s momentum (which is the bullet weight multiplied by the straight velocity, not the square of the velocity), contributes to greater “stopping power” or “knockdown power.” This is, after all, essentially the classic “9mm vs. .45” debate.

Need for Speed, or Heavy Metal?

So which side is right? What is more effective at stopping a threat? Lighter, faster bullets with their explosive cavitation, or heavier, slower bullets with their “knockdown power?” Or is it the middle-weight, just-right Goldilocks bullet? Well, according to the hard science on the matter, no one is right, and none of this really matters. Research has continuously shown that temporary cavitation does not contribute in a significant way to wounding unless certain types of tissues (liver and brain tissue, for example) are seriously affected by it. It just looks really cool in ballistics gel. Further, the argument that the high-energy rounds “deposit more energy” into the target appears to be scientifically baseless, at least as far as that energy contributing to stopping a threat. The law of conservation of energy requires that it goes somewhere, but that doesn’t mean it actually does any extra meaningful damage in elastic tissues). Lastly, research also shows that there is seemingly no such thing as “knockdown power” in any handgun round, even the good old .45. There is some argument to be made that a wider bullet (like a .45) does more damage, as it creates a slightly larger permanent wound cavity. But that is more than offset by the higher capacity and lower recoil (allowing more shots on target) that a smaller bullet (like a 9mm) will generally have.

The most important consideration in whether or not a handgun round will stop a threat is penetration. The bullet simply must penetrate deep enough to hit the significant bits. Expansion is the runner-up, as it helps prevent dangerous overpenetration and contributes to the permanent wound cavity. The FBI standard is that a bullet must penetrate at least 12 inches, but ideally should not penetrate over 18 inches, in standard ballistics gel. But the thing is, pretty much every popular bullet weight in any adequate self-defense cartridge is capable of penetrating 12 inches and expanding just fine, and that is the only thing that counts. This means that, at least as far as effectiveness at stopping a threat, bullet weight really doesn’t matter.

What Weight DOES Affect

Even though any of the available weights of the common, proven bullets will do an essentially equal job of stopping a threat, there are still other effects of bullet weight that every shooter needs to know, and that can make a real difference. Bullet weight can affect point of impact, accuracy, and recoil impulse, so it is essential that you train with whatever cartridge you choose to carry, at least every so often. If you only shoot cheap 115gr round nose through your 9mm but carry 147gr HST, you don’t want to learn about these potential differences for the first time when you’re in the middle of a gunfight.

First, point of impact. Different bullet weights will generally hit different spots on the target. Usually, heavier bullets will hit higher, and lighter bullets will hit lower. This occurs because the heavier, slower bullet takes a tiny bit longer to leave the barrel, during which time the muzzle is moving upward from recoil. Accordingly, the gun ends up pointed slightly higher when the bullet actually leaves the muzzle. Velocity and recoil matter too of course, as this is actually a function of velocity and recoil is what raises the muzzle in the first place. But if you’re shooting comparably powerful loads such as defensive loads, the heavier bullets will almost always be moving more slowly as previously discussed. This matters for self-defense; a point of impact that differs significantly from your point of aim can mean a miss, and this is more pronounced the further away your target is. Chances are your carry gun has fixed sights, and these fixed sights are going to work best with a particular bullet weight. Generally, this is whatever the most common target load is for that caliber. You need to know if your chosen carry load’s point of impact may differ from your sights’ point of aim at a variety of distances, and if so, how significant the difference is.

Second, there is accuracy. As all bullets for the same caliber are by definition the same diameter, the heavier bullets must be longer in order to be heavier (except when there are differences in materials – lighter weight, all copper bullets are also long, for example). Different guns can be more accurate or less accurate with different loads, and the length and weight of the bullet can affect this. Other things can affect this as well, like the shape of the bullet or the features of your gun and its rifling. The lesson, though, is that you may get better accuracy with one bullet weight over another, even in the same brand. You may also get differences in accuracy with the same weight bullets from different brands. So, in addition to testing your carry ammo thoroughly for reliability, as is always recommended, you should also be sure to make a note of its relative accuracy. You don’t want to miss when it matters.

Third, there is the issue of recoil impulse. A heavier bullet will not always have more recoil than a lighter bullet, as many factors come in to play. Velocity, energy, and even the burn rate of the specific powder used can contribute to differences in felt recoil. However, different bullet weights even in the same line of ammunition can have different recoil impulses, and the way people experience recoil can be highly subjective. Again, the important thing is to be familiar with how your chosen carry load recoils, and to train with it, so that it doesn’t take you by surprise.

And finally, it is essential to know how your gun’s barrel length can affect the performance of a given load. A heavy bullet out of a very short barrel might not have enough velocity to expand, and a lighter bullet out of a longer barrel might expand too quickly and underpenetrate. Conversely, because lighter bullets require more powder to achieve the desired pressure and velocity, a short barrel may not allow enough dwell time in the barrel for adequate pressure and velocity to be reached. For most guns with “average” length barrels it is not as much of a concern, but for short barreled guns, it can make a big difference, which is why there are so many short-barrel-specific loads on the market. If you carry a full-size gun, you also need to be wary of using a load designed with short barrels in mind, as they often expand too quickly at the higher velocity they achieve in a long barrel or fail to achieve as much velocity as other loads would from that longer barrel. There are a lot of factors at play here, but it is important to look for tests of any given load that are done with a gun having a similar barrel length to yours.

Weighing Your Options

If you take all of the above considerations into account, the most important thing is to train with whatever you pick adequately. Make sure it is reliable, make sure it hits where you point the sights (or at least know how you need to adjust your aim at different distances), make sure it is accurate, and make sure you can handle the recoil well.

Still, you have to pick one to start. It is probably best to start with a “middle of the road” bullet weight and work from there. For 9mm, that would be a 124-grain load. 147-grain seems to be very popular these days (no doubt due in part to the “bigger number = better” mentality), but there are certain caveats you need to be aware of with that choice. Most people will do most of their practice with the cheapest, most common 115-grain ball ammo, and their gun’s fixed sights (or at least the way they hold them in relation to the target) are likely to be adjusted for that load. A 147-grain defensive load can have a significant difference in point of impact and recoil than that 115-grain ball, so it is important to know what those differences are and to train with that 147- grain load frequently.

Also, it is important to keep in mind that the 147-grain load is no more effective in any measurable way over a 124-grain or 115-grain load that penetrates similarly and expands reliably. If your gun is dead on with those 115-grain ball loads and you shoot them well, why not try a 115-grain defense load if that load performs? There is no shame in shooting a lighter bullet, despite any implied machismo or “my number is bigger than yours” talk.

Some manufacturers understand the issue of disparities between practice ammo and carry ammo, and that provide options. For example, Speer makes their excellent Gold Dot hollow points in 115, 124, and 147-grain offerings, and they also make their Lawman line of practice ammo in all three weights as well. Lawman is also loaded to similar velocities, so that training with the cheaper practice ammo more accurately simulates how the Gold Dots will shoot. If you’re a shrewd shopper, you do your research, and you don’t mind spending a little more money than whatever is the absolute cheapest at the time, it is definitely possible to find an inexpensive practice load that most closely simulates your carry load.

As expensive and time-consuming as trying different premium carry loads can be, look on the bright side. It is a valid excuse to go to the range and shoot more!