Biting the Silver Bullet-18

Aim to Impact: Six Factors that Influence Shooting Accuracy

By Sanjay Soni

There are several factors that influence the accuracy and performance of ammunition.

1.         Grain Weight of the bullet

2.         Case design and material

3.         Type of firearm being used

4.         Type of ammunition being used

5.         Weather Conditions

6.         Tolerances That Affect Ammunition and Rifle Performance

Let us take a look at each of these to understand how they affect the accuracy of your shots.

1. How Grain Affects Accuracy and Performance in Ammunition

When it comes to ammunition, the weight of the bullet is a crucial factor that affects its accuracy and performance. Measured in grains, the weight of a bullet can determine its velocity, trajectory, and terminal ballistics, making it a significant factor in the overall performance of a firearm.

In this section, we will explore how grain affects accuracy and performance in ammunition.

a. Velocity

The weight of a bullet can affect its velocity, as lighter bullets tend to travel faster than heavier ones. However, higher velocity can also result in a less stable trajectory, making it more difficult to hit the target accurately.

On the other hand, heavier bullets tend to have lower velocity but a more stable trajectory, making them a better option for long-range shooting. Ultimately, the velocity of a bullet must be balanced with its weight to achieve optimal accuracy and performance.

b. Trajectory

The weight of a bullet can also affect its trajectory, which is the path it takes from the barrel of the firearm to the target. A heavier bullet will typically have a flatter trajectory, meaning it will maintain its trajectory for a longer distance before dropping. This can be beneficial for long-range shooting.

A lighter bullet may have a more curved trajectory, making it a better option for shooting at shorter distances. The trajectory of a bullet must be considered when selecting the appropriate grain weight for a particular firearm.

c. Terminal Ballistics

The weight of a bullet can also affect its terminal ballistics, which is the behavior of the bullet upon impact. Heavier bullets tend to have more kinetic energy upon impact, resulting in greater transfer of energy to the target. This can be beneficial for hunting or self-defence, as it increases the likelihood of stopping the target.

Conversely, a lighter bullet may penetrate the target more deeply, resulting in a higher likelihood of hitting vital organs. The terminal ballistics of a bullet must be considered when selecting the appropriate grain weight for a particular situation.

d. Comparing Options

When selecting the appropriate grain weight for a firearm, it is important to consider the intended use of the ammunition. For example, a heavier bullet may be a better option for long-range shooting, while a lighter bullet may be more suitable for self-defence situations. It is also important to consider the firearm itself, as some firearms may be better suited for certain grain weights.

Ultimately, the grain weight of a bullet must be balanced with other factors, such as velocity, trajectory, and terminal ballistics, to achieve optimal accuracy and performance.

How grain affects accuracy and performance in ammunition

2. The Impact of Bullet Case Design on Accuracy and Performance

The bullet case design is an essential aspect of ammunition production that is often overlooked.

The design of the case has a significant impact on the accuracy and performance of the bullet. In this section, we will explore the factors that affect the design of bullet cases and their impact on accuracy and performance.

1. Case Length

The length of the case plays a crucial role in determining the accuracy of the bullet. A shorter case results in a smaller powder capacity, which can lead to a decrease in velocity and accuracy. On the other hand, a longer case can increase the powder capacity, resulting in higher velocity and accuracy.

However, longer cases may not fit in some firearms, and reloading longer cases requires special dies.

• Case Wall Thickness

The thickness of the case wall affects the strength and durability of the case. A thicker case wall can withstand higher pressure, resulting in higher velocity and accuracy.

However, thicker case walls increase the weight of the cartridge, which can affect the trajectory of the bullet. Thinner case walls reduce the weight of the cartridge, resulting in a flatter trajectory, but they are not as durable and can deform under high pressure.

1. Case Material

The material used to make the case affects its strength, durability, and weight.

Brass is the most common material used for bullet cases due to its strength, durability, and ability to expand and contract during firing. Steel cases are cheaper but not as durable or malleable as brass. Aluminum cases are lightweight but not as strong or durable as brass or steel.

• Case Neck

The neck of the case holds the bullet in place and affects the amount of tension applied to the bullet. A tighter neck provides more tension, resulting in better accuracy, but it can also increase pressure. A looser neck reduces pressure but can result in decreased accuracy.

• Primer Pocket

The primer pocket holds the primer in place and affects the ignition of the powder. A tight primer pocket can result in more consistent ignition, resulting in better accuracy.

A loose primer pocket can cause misfires or inconsistent ignition, resulting in decreased accuracy.

Overall, the best bullet case design depends on the specific application and firearm. For example, a hunter may prefer a lighter-weight cartridge with a flatter trajectory, while a long-range shooter may prefer a heavier cartridge with higher velocity and accuracy.

It is essential to consider all these factors when selecting the best bullet case design for your specific needs.

3. Type of Firearm Being Used

Different firearms have different levels of accuracy and shooting speed. From the calculated precision of a sniper rifle to the rapid response of a handgun, each type of firearm serves a unique purpose.

Sniper rifles and their ammunition are engineered for long-distance engagements. In stark contrast, handguns are optimized for close-quarters combat efficiency. Designed for swift draw times and rapid-fire capabilities, these compact firearms excel in situations where speed is paramount.

Whether navigating tight urban environments or engaging in sudden, unexpected confrontations, a well-trained individual with a handgun can quickly neutralize threats with precise close-range shots. The compact nature of handguns allows for easy manoeuvrability, making them a preferred choice for those anticipating dynamic, fast-paced encounters where split-second decisions can mean the difference between life and death.

4. Type of Ammunition Being Used

The type of ammunition being used can also play a role in bullet speed and accuracy. Each type of ammunition serves a specific purpose, whether it be for target shooting, self-defence, hunting, or military applications. Understanding their differences is crucial for firearm users to make informed decisions based on their circumstances and needs.

1. Full Metal Jacket ammunition (FMJ) is often favored for military applications due to its reliability and ability to pierce body armor. These rounds feature a soft lead core encased in a harder metal, such as copper or steel. However, they are less effective at causing rapid expansion upon impact, making them less ideal for hunting or self-defence.

• Hollow Point (HP) ammunition is designed for maximum stopping power. These rounds have a hollow cavity at the tip, which allows them to expand upon impact. When the bullet strikes a target, the hollow point mushrooms outward, creating a larger wound channel and transferring more energy to the target. This design makes HP rounds highly effective for self-defence and hunting, as they are more likely to incapacitate a threat or takedown game animals quickly. However, they are typically more expensive than FMJ rounds and may not feed as reliably in some firearms.

• Unlike the bullets used in handguns and rifles, shotgun ammunition comes in the form of shells. Shotgun shells contain multiple pellets, also known as a shot or a single slug. Shotguns are versatile firearms, capable of firing a variety of loads depending on the intended use. Birdshot, which consists of numerous small pellets, is commonly used for hunting birds and small game. Buckshot, larger pellets designed for increased stopping power, are favoured for self-defence and hunting larger game. Slug rounds, on the other hand, are solid projectiles used for hunting big game at closer ranges or in situations where greater penetration is needed.

5. Weather Conditions

Weather conditions such as wind, rain, and humidity can also affect bullet speed and accuracy. Wind can cause the bullet to veer off course, while rain and humidity can affect the bullet’s trajectory. These factors are often unpredictable.

To illustrate, let’s take the example of a person who is trying to dodge bullets in an open field. If the shooter is using a sniper rifle from a distance, the target may have more time to react and dodge the bullet. However, if the shooter is using a handgun from a close range, the target may have less time to react and dodge the bullet. Additionally, if the weather conditions are windy, the bullet may be more likely to veer off course, making it even more difficult to dodge.

The distance between the shooter and the target can greatly affect bullet speed and accuracy. At long distances, the bullet is more likely to lose velocity and accuracy due to weather conditions, making it easier to dodge. On the other hand, if the shooter is too close, the target may have less time to react and dodge the bullet.

When it comes to long-range shooting, one of the most challenging aspects is mastering wind calls. The wind is a formidable adversary that can significantly affect the trajectory of a bullet, making it crucial for precision shooters to understand and account for its influence.

Let’s delve into the various factors that come into play when dealing with wind calls, exploring different perspectives and providing in-depth information to help shooters hit their mark with confidence.

a. Wind Speed and Direction Wind speed and direction are the fundamental factors that determine how much the wind will impact a bullet’s flight path. Understanding the wind’s velocity and angle is essential for accurate wind calls. Shooters must assess the wind at various distances between themselves and the target, as the wind can vary in intensity and direction at different points along the bullet’s trajectory. An experienced shooter knows that even a slight change in wind speed or direction can lead to significant deviations in bullet impact. For instance, let’s consider a scenario where a shooter is engaging a target 1000 yards away. At the shooter’s position, the wind might be blowing at 10 mph from the left. However, halfway to the target, the wind could be gusting at 15 mph from the right. Such variations require the shooter to make precise adjustments to compensate for the changing wind conditions.

b. Wind Angle The angle at which the wind is blowing relative to the bullet’s flight path plays a vital role in determining the amount of drift the bullet will experience. Headwinds and tailwinds have different effects on bullet trajectory compared to crosswinds. A headwind slows down the bullet, causing it to drop more rapidly, while a tailwind has the opposite effect, increasing the bullet’s velocity and reducing the amount of drop. Crosswinds, on the other hand, push the bullet sideways, causing it to drift off course. Imagine a shooter aiming at a target with a crosswind blowing from left to right. The shooter must compensate by holding slightly into the wind, adjusting their aim to counteract the lateral drift caused by the crosswind. Failing to account for wind angle can result in missed shots and frustration.

c. Wind Mirage Wind mirage is the visual distortion caused by varying air densities along the bullet’s path. This can make it challenging to accurately gauge the wind’s effects on the bullet’s trajectory. Shooters often use mirage patterns to estimate wind speed and direction. By observing how the mirage moves or shimmers, experienced shooters can make more informed wind calls. For example, a skilled shooter might notice that the mirage appears to be moving slowly from left to right, indicating a light breeze blowing in that direction. By using this information in conjunction with other factors, such as wind flags or vegetation movement, the shooter can refine their wind call and make adjustments accordingly.

d. Terrain Effects The terrain over which the bullet travels can significantly influence wind patterns and, consequently, the bullet’s trajectory. Features such as hills, valleys, buildings, or dense foliage can create wind tunnels or cause turbulence, altering the wind’s behavior. These terrain effects can be particularly challenging for long-range shooters, as they introduce unpredictable variables into the equation. Let’s consider a scenario where a shooter is positioned on top of a hill, engaging a target downhill. As the wind hits the slope, it may rise or fall, creating an upward or downward draft that affects the bullet’s flight path. In such cases, shooters must carefully analyze the terrain to make accurate wind calls. Mastering wind calls is a skill that takes time, practice, and a deep understanding of the various factors that affect bullet trajectory. By considering wind speed and direction, wind angle, wind mirage, and terrain effects, long-range shooters can make more precise adjustments to compensate for the wind’s influence. Through experience and observation, shooters can develop a keen sense of wind calls, enabling them to consistently hit their mark at extended distances.

6. Tolerances That Affect Ammunition and Rifle Performance

 

As we explore both ammunition and firearms mass production techniques and tolerances, we need to understand that when millions of anything are being manufactured, it is impossible to make them all the same. That’s why there are tolerance ranges around a specification or standard.

Imagine you set a velocity standard of 2,600 feet per second (fps). Because of the variables involved, you have to allow a tolerance of +/- 30 fps. The manufacturer will test samples before loading this ammunition. If rounds test between 2,570 to 2,630 fps, that would be considered as acceptable.

The same applies to the groove dimensions of a barrel. If the minimum-allowable diameter is .3080 inch, then the manufacturer has to allow some tolerances that they can maintain in production, say .3095 inch. Any barrel’s groove diameter that measures from .3080 to .3095 inches would be considered as acceptable.

The ammunition and the firearm are a system. One affects the other and vice versa. There are certainly manufacturing tolerances in ammunition that affect performance. There are also a number of dimensional tolerances in firearms that have a significant impact on ammunition performance.

Let’s start by examining production issues that can occur with ammunition.

Establishing Standards 

Ammunition manufacturers go to extreme lengths to control variables when testing ammunition. This effort dates back to 1926 when the Sporting Arms Ammunition Manufacturers Institute (SAAMI) was organized by ammunition and firearms companies to establish and maintain production standards and specifications for ammunition and firearms.

SAAMI has established test-barrel dimensions and chambers with extremely tight tolerances. Test barrels are meticulously measured and calibrated with reference ammunition to ensure that testing equipment produces consistent results across the entire industry. If a barrel does not conform to the dimensional specifications or does not produce the desired performance with reference ammunition, it is discarded. Test barrels are retested with reference ammunition at regular intervals and if they are not within the performance specifications, they are removed from service.

As an example of how a very simple thing can affect ammunition performance, let’s look at barrel length. The test barrel length for virtually all SAAMI standardized rifle cartridges and the barrel length used for advertising rifle ammunition is 24 inches.

Would you expect the Browning X-Bolt Micro with a 20-inch barrel to produce the same velocity as the 26-inch barrel on the X-Bolt Hell’s Canyon Long Range of the same caliber? A rifle with a barrel that is shorter than 24 inches will shoot slower than advertised with factory ammunition.

Manufacturers test ammunition at regular intervals to ensure performance is held as close to these specs as possible.

1. Ammunition Variables

Ammunition manufacturing involves many variables. Projectile diameter can vary by several tenths of a thousandth over a production run of millions of projectiles. Cartridge case capacity, dimensions, and hardness can also vary slightly over production runs of millions of pieces.

Consider the SAAMI drawing for the .308 Winchester, for example. SAAMI drawings always show the dimensions for a cartridge with a maximum dimension with a minus tolerance and a minimum dimension chamber with a plus tolerance. You can see that the cartridge dimensions can have fairly large differences in dimensions and still be an in-spec cartridge.

Of course, whenever these dimensions vary, the performance will differ slightly.

Propellant performance can also vary from container to container. Keep in mind that propellant is also mass-produced at tens of thousands of pounds at a time, but can only be blended into the final product several thousand pounds at a time. The performance across an entire lot of propellant invariably varies a little.

Expect a 30-to-50 fps variation in ammunition because of the variables mentioned above. Manufacturers do their best to control these variables and adjust for them during a production run. If the goal was to load every cartridge to the same performance, little would be produced and no one could afford to purchase it. This is where handloading comes in.

Ammunition manufacturers deal with these issues by establishing performance specifications and tolerances on velocity and pressure for production loading ammunition.. They will test at regular intervals to ensure that the ammunition performs within this tolerance range. At any test firing, if ammunition does not perform within the tolerance range, adjustments will be made.

So, what are these tolerances?

SAAMI allows a +/- 90 fps tolerance range on rifle ammunition velocities from the standard published velocity. This is a pretty significant range and leads us into tolerance ranges that manufacturers use.

If you are purchasing low-cost ammunition, a manufacturer will generally use most of the SAAMI +/- 90 fps velocity tolerance. It allows them to test less and keep the production machine running longer before stopping for adjustments. This lowers the cost.

At the other end of the spectrum, if you purchase high-cost, premium ammunition, the manufacturer will generally have a much tighter tolerance range on performance to justify the higher cost and higher performance expectation. Velocity tolerances on premium or match-grade ammo are usually in the +/- 20 to 40 fps velocity range.

Remember, the ammunition could still be 20 fps slower than the advertised velocity, and it could also be 20 fps above the advertised velocity. Like I said, nothing can be mass-produced by the millions to be exactly the same.

• Firearms & Variance

Just like ammunition, it is virtually impossible to mass-produce firearms that are all exactly the same and have exactly the same dimensions. As in ammunition, firearm manufacturers have dimensional tolerance ranges that are used during production.

Raw materials can vary slightly from lot to lot. Tooling wear, such as wear on a chamber reamer or rifling tooling is a big issue for barrel manufacturers. Lathe or mill accuracy and repeatability must all be considered. These issues force manufacturers to establish a tolerance range for virtually any dimension of a firearm.

Bore and Groove Dimensions

There are two sets of dimensional tolerances in firearms that have a significant effect on ammunition performance. The first is bore and groove dimensions. Ammunition manufacturers religiously use the SAAMI minimum dimensions for safety and uniformity. A firearms or barrel mass producer cannot economically produce barrels that are all made to the absolute minimum bore and groove dimensions. The costs to manufacture and gauge barrels to these minimum dimensions would be astronomical.

This is not to say that mass-produced barrels are of poor quality or even sloppy. With recent advancements in machine and production processes, the tolerance on bore and groove dimensions is considerably tighter than 25 years ago. Hammer forging of barrels has been a major factor in improving the dimensional quality of mass-produced barrels.

Typical bore and groove dimension tolerances in mass-produced barrels are about +.001 to .0015 inches above minimum.

Large grooves can allow the projectile to tilt or yaw in the bore. This yaw will be present when the projectile exits the barrel, which degrades a projectile’s accuracy.

This phenomenon works in the opposite direction, too. Groove dimensions larger than the minimum dimension cause pressure and velocity to decrease.

Other Tolerances

The other dimensional tolerances in a firearm that can have a large effect on ammunition and rifle performance are the chamber reamer and consequently, chamber dimensions.

If you consider the SAAMI .308 Winchester drawing, you will see that the chamber dimension tolerances are pretty generous, +.002 inches in diameter and .015 inches in length. Firearms manufacturers will use reamers near the maximum dimensions on a new reamer to extend the life of the reamer and reduce production costs. This way, as the reamer wears and gets dull, they can sharpen it several times and get more life out of the tool and reduce production costs.

If you get a rifle that is near the maximum of the reamer/chamber dimensions, the chamber and throat are going to be rather big. This causes energy loss, swelling of the case, gas blowby around the projectile, increased jump to the rifling and a loss in pressure and velocity.

Gas-operated semiautomatic firearms can also cause small losses in ammunition performance. Some of the gas that would otherwise be pushing the projectile is bled off to operate the action.

Revolvers present a whole different set of dimensional tolerance challenges that affect performance. The forcing cone dimensions can allow gas to escape around the bullet. Cylinder gap variations can cause fluctuations in gas lost out of the gap. Small differences in these dimensions can have a significant effect on the performance ammunition will produce.

Hopefully, after reading this you will have an appreciation for the many things that affect firearms and ammunition performance in combination. The next time you want to dispute marketing and sales numbers as inaccurate, remember the factors that can affect those nominal specifications. To all of us that choke when looking at custom gun prices, remember to stop and think about why such guns cost so much. Generally, when you buy a custom-made firearm, you are paying for the extra effort to control all the variables discussed above to a much higher level than can be done in mass production.

Sanjay Soni is the Managing Director of Hughes Precision Manufacturing Pvt. Ltd., India’s first small-caliber 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 9 years.