By Sanjay Soni
In continuation to the earlier article where we discussed the lethality of different firearms, we will now delve into the stopping power of different bullet weights. That has a significant impact on the final outcome of a shot fired whether it is from a handgun or a rifle.
If you’re a new gun owner, you probably don’t know what “bullet grain” means. You may look at a box of ammo, see “115-grain” written on the side, shrug, and flip it over to look at what you really care about: the price tag. Before you do that, take some advice from a few seasoned firearm experts and consider the ammunition grain you’re purchasing.
What Is ‘Bullet Grain’?
A grain (“gr” for short) is a basic unit of weight measurement. One grain is equal to 1/7,000 of a pound or 1/437.5 of an ounce.
All bullets are classified based on their weight in grains. For example, the most common 9mm Luger cartridges have bullet weights of 115 grains, 124 grains, 147 or 158 grains.
A common misconception of the term “grain” on the ammo box is that it is a reference to the amount of gunpowder in the cartridge. To be fair, gunpowder is also measured in grains if you’re into hand-loading. The label, however, is strictly speaking about the weight of the bullet–the projectile that exits the barrel.
Now that we’ve covered the basics of what “grain” refers to, take a look at how you can use that knowledge to improve your shooting.
What Effect Does Bullet Grain Weight Have On Shooting?
The weight of the bullet influences its performance. A light bullet has less energy and is more vulnerable to wind. It may be blown off target far more readily than a heavier bullet. In terms of precision, neither is clearly superior. It all depends on your shooting style and what you value most in a bullet.
The relationship between bullet weight and velocity is complex but generally agrees with the following equation: V = k x w Where V is velocity, k is a constant for each particular cartridge, w is weight in grams, and V is measured in meters per second (m/s).
Based on this equation, we can see that heavy bullets will produce higher velocities. This is because there’s more mass attached to the end of the bullet, so it will take longer
to stop when it hits something. Heavy bullets are also better at holding their shape during flight, which allows them to travel farther before collapsing under their own weight. Finally, heavy bullets tend to have more surface area, which inflicts more damage as the bullet enters the body.
As for light bullets, they’re not suitable for use with every firearm, especially those that don’t have an internal mechanism for spinning the bullet as it leaves the barrel. These include many older designs and some modern replicas.
Is A Higher Grain Bullet Better?
Lighter bullet weight often implies faster and further travel, but also greater recoil and less power at the target. For competitive and long-range shooting, lighter rounds are preferable. Heavier weight equals more efficacy, making them ideal for defense, huge game, and conflict. Of course, the opposite is true as well – heavy bullets are preferred for close-up work and animal hunting.
It’s all about trade-offs. If you need/want a fast bullet that gives you much recoil, then a heavier bullet is recommended. A heavy bullet will tend to stop more quickly than a light one, giving you time to adjust your aim before the target moves out of range. On the other hand, if you want a low-recoil bullet that doesn’t necessarily go far, then a light bullet is better. The key here is to find a balance between speed and control that works for you.
In general, higher grain means faster velocity and therefore faster travel and reduced size on impact. However, this comes with the cost of increased recoil. So, not only do you get more energy out of each shot, you also feel it in your shoulder too! However, weapons with longer barrels and newer technology can lower the recoil significantly. Going subsonic also lowers the recoil felt by the shooter.
Most special forces use heavy subsonic bullets with their suppressed weapons.
Subsonic cartridges are loaded to operate at speeds less than the speed of sound, which prevents the bullet from making a supersonic shockwave or “crack” as it travels through the air.
When used in conjunction with suppressors, the subsonic bullet significantly reduces the total sound signature of the firearm, as the majority of the muzzle blast is suppressed by the silencer, while the lower velocity projectile removes the supersonic crack. The only audible noise would come from the mechanical moving parts made by the firearm, aside from the noise produced by the escaping gases at the muzzle end.
The downside is that subsonic ammo reduces the effective range and stopping power of the firearm, while also incurring a much steeper trajectory. For this reason, subsonic ammunition usually uses heavier bullets that retain more energy and momentum. If you would normally go with a 124gr 9mm bullet at supersonic speed, you would need a 147gr or 158gr to achieve similar results at subsonic speeds.
Let’s deep dive a bit into how you can calculate the ballistics of a bullet:
External Ballistics (From Gun To Target)
The external ballistics of a bullet’s path can be determined by several formulae, the simplest of which is:
Kinetic Energy (KE) = 1/2 MV2
Velocity (V) is usually given in feet per second (fps) and mass (M) is given in pounds, derived from the weight (W) of the bullet in grains, divided by 7000 grains per pound times the acceleration of gravity (32 ft/sec) so that:
Kinetic Energy (KE) = W(V)2 / (450,435) ft/lb
This is the bullet’s energy as it leaves the muzzle, but the ballistic coefficient (BC) will determine the amount of KE delivered to the target as air resistance is encountered.
Forward motion of the bullet is also affected by drag (D), which is calculated as:
Drag (D) = f(v/a)k&pd2v2
f(v/a) is a coefficient related to the ratio of the velocity of the bullet to the velocity of sound in the medium through which it travels. k is a constant for the shape of the bullet and & is a constant for yaw (deviation from linear flight). p is the density of the medium (tissue density is >800 times that of air), d is the diameter (caliber) of the bullet, and v the velocity. Thus, greater velocity, greater caliber, or denser tissue gives more drag. The degree to which a bullet is slowed by drag is called retardation (r) given by the formula:
r = D / M
Drag is difficult to measure, so the Ballistic Coefficient (BC) is often used:
BC = SD / I
SD is the sectional density of the bullet, and I is a form factor for the bullet shape. Sectional density is calculated from the bullet mass (M) divided by the square of its diameter. The form factor value I decreases with increasing pointedness of the bullet (a sphere would have the highest I value).
Since drag (D) is a function of velocity, it can be seen that for a bullet of a given mass (M), the greater the velocity, the greater the retardation. Drag is also influenced by bullet spin. The faster the spin, the less likely a bullet will “yaw” or turn sideways and tumble in its flight path through the air. Thus, increasing the twist of the rifling from 1 in 7 will impart greater spin than the typical 1 in 12 spiral (one turn in 12 inches of barrel).
Bullets do not typically follow a straight line to the target. Rotational forces are in effect that keep the bullet off a straight axis of flight. These rotational effects are diagrammed below:
Yaw refers to the rotation of the nose of the bullet away from the line of flight. Precession refers to rotation of the bullet around the center of mass. Nutation refers to small circular movement at the bullet tip. Yaw and precession decrease as the distance of the bullet from the barrel increases.
What Do All These Formulae Mean In TermS Of Designing Cartridges & Bullets?
Well, given that a cartridge can be only so large to fit in a chamber, and the steel of the chamber can handle only so much pressure from increasing the amount of gunpowder, the kinetic energy for any given weapon can be increased more easily by increasing bullet mass. Though the square of the velocity would increase KE much more, it is practically very difficult to increase velocity, which is dependent upon the amount of gunpowder burned. There is only so much gunpowder that can be burned efficiently in a cartridge. Thus, cartridges designed for hunting big game animals use very large bullets.
To reduce air resistance, the ideal bullet would be a long, heavy needle, but such a projectile would go right through the target without dispersing much of its energy. Light spheres would be retarded more within tissues, releasing more energy, but might not even get to the target. A good aerodynamic compromise bullet shape is a parabolic curve with low frontal area and wind-splitting shape.
Why Choose A Heavy Bullet?
As we have seen earlier, the two major variables in handgun ballistics are diameter of the bullet and volume of gunpowder in the cartridge case. Cartridges of older design were limited by the pressures they could withstand, but advances in metallurgy have allowed doubling and tripling of the maximum pressures so that more KE can be generated. Many different cartridges are available using different loads and bullet designs. Some of these are outlined in the table below to compare and contrast the ballistics.
|COMMON REPRESENtAtIVE HANDGuN CARtRIDGES|
|Bullet Weight (grains)||Velocity (muzzle) in fps||Energy (muzzle) in ft lbs||Energy (at 100 yd) in ft-lbs|
|for inexpensive guns, rimfire (R and A)|
|small pocket gun (A only)|
|popular pocket auto(A only)|
9 mm para
|popular military handgun(A only)|
|popular police revolver(R only)|
|popular police pistol(A only)|
.357 mag- num
|popular police and hunting re- volver(R and A)|
|rimless police pistol(A only)|
|same projectile as.40 S&W(A only)|
|.44 mag- num||hunting revolver (R only)|
|popular military handgun(R and A)|
|cowboy “sixgun” (R only)|
|Big game and metallic targets (A only)|
|Key: R=made for revolver; A=made for semi-automatic; velocity in fps|
What Can Be Learned from Specific Cartridge Data?
If the 44 magnum is compared with the 357 magnum, the effect of bore diameter is evident. The larger area of the 44 magnum creates more force with the same pressure, allowing the 44 magnum to produce more energy at the muzzle. The effect of case capacity can be demonstrated
in a comparison of the 9 mm Parabellum (para) with the 357 magnum. These cartridges have similar diameters and pressures, but the 357 magnum is much longer, yielding more case volume (more powder), and delivering more energy. Finally, despite the Colt 45 having the largest bore diameter and one of the longest cases, it does not deliver the maximum energy because the outdated 1873 design of this cartridge case severely handicaps its pressure handling capability.
The most important reason for selecting a larger bullet is the energy delivered to the target, which improves “terminal ballistics.” Basically, if you want better expansion and penetration you will likely want to choose a heavier bullet. Both expansion and penetration are affected by bullet shape, material, and other factors as well, but weight plays a role.
This essentially means that in most cases heavier bullets are reserved for hunting and self defense. When loaded into hunting rifles, a heavier bullet is more likely to deliver more energy into the target, resulting in a more humane shot. For self defense, a heavier bullet gives you a better chance at stopping a threat.
There are people who swear by a heavier bullet weight in their self defense rounds. The Federal Bureau of Investigation (FBI) recently selected Hornady Critical Duty .40 S&W 175 grain as their bullet of choice.
This issue came up in the trials of 9mm 158gr subsonic ammunition being conducted by the armed forces. Two companies offered the 147gr 9mm subsonic ammunition instead of the 158gr ammunition stating that the ballistic properties are the same as that of the 158gr ammunition. They achieved subsonic shots with lighter rounds by reducing the quantity of powder to a very low level, which is not safe. This was of course a totally misleading claim made by the companies who did not have the 158gr ammunition in their product line up. Since the subsonic ammo was to be used with a suppressed MP-5 by the special forces, even a difference of 11 grains would make a huge difference in the performance of the ammo:
- The kinetic energy of the bullet as well as the terminal ballistics are very different between the 147gr and 158gr bullets. The heavier 158gr bullet carries much more energy and so the terminal effect would be more pronounced.
- The sound produced by the 158gr bullet would also be less pronounced than that made by the 147gr ammo.
- Unless you have a short barrel, the 147gr bullet will break supersonic out of a 16” barrel. To prevent that you would drop the powder charge to a minimum which is not only unsafe but would also lead to a perceptible drop in the bullet trajectory even over a short distance. So accuracy would be a major issue!
- The 158gr bullet has a higher ballistic coefficient and higher sectional density which would cause much more damage upon entry into the target. Therefore, lethality and stopping power would be much more pronounced in a 158gr bullet as compared to a 147gr bullet.
- The only reason 158 gr. 9mm even exists is so 9mm rifles/carbines can fire a round that will still stay subsonic even though the barrel is longer. With a 147gr bullet, the subsonic is not guaranteed.
Shockingly, the person doing the testing also seemed to buy into this argument that the bullet weight of 147gr would perform the same as a 158gr!!! It seems that most people – even those in charge of testing ammo for the armed forces – are unaware of the behavior of bullets with different grain weights.
Many law-enforcement agencies are starting to choose rounds on the heavier side. As previously mentioned, the FBI selected the Hornady Critical Duty 175-grain .40 S&W as its preferred ammo. When you think about how your choice in bullet weight will affect your shooting, keep these things in mind:
X Lighter weight generally means more speed and distance, but also more recoil and less power at the target. Lighter bullets are good for competition and long-range shooting.
X Heavier weight generally means more effectiveness, making them excellent for defense, large game, and combat. Added benefit is that heavier bullets generally have higher Ballistic Coefficient’s and always have higher sectional density for a given caliber.
Sanjay Soni is the Managing Director of Hughes Precision Manufacturing Pvt. Ltd., India’s first small calibre manufacturer in the private sector. An MBA from the Indian Institute of Management, Bangalore, he has been involved with the ammunition industry in India and abroad since the last 8 years.