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When it comes to choosing an air rifle, shooting enthusiasts have a variety of options to choose from, including different calibres like 4.5mm and 5.5mm. These are the only two legal calibres for air rifles in South Africa. Each calibre has its characteristics that cater to specific preferences and shooting purposes, it is very important to understand these unique characteristics before making a purchasing decision. 
 
In this blog, we’ll explore the main differences between the 4.5mm and the 5.5mm calibre option, their advantages, disadvantages, and scenarios where each of them outdoes the other. 
 
Understanding Calibre 
 
Before going into detail about the characteristics of the 4.5mm and the 5.5mm air rifles, we’ll quickly discuss the concept of calibre. The calibre of an air rifle refers to the internal diameter of the barrel of an air rifle and is typically measured in millimetres or inches. 4.5mm is also commonly known as .177 and 5.5mm is commonly known as .22. It is an important factor that determines the size and the type of pellet that will be used and directly influences the air rifle's accuracy, power, and trajectory. Smaller calibre air rifles have narrower barrels, while a larger calibre has a wider barrel. 
 
A Common differentiator between the two calibres is the common Moncur “4.5 for feathers, 5.5 for fur” This is a great way of deciding which calibre to purchase. 4.5mm air rifles are more commonly used for pest control in terms of small bird and rodents whereas 5.5mm is used for hunting small game. A .22 air rifle with the right power and ammunition has the capability of taking out the larger game. 
 
Furthermore, it is important to fully understand the advantages and disadvantages of each calibre. While many shooters have a preference for one or the other, there is always a best-case scenario, which is what we will explore.  
 
4.5mm Air Rifles 
 
Advantages: 
 
1. High Velocity: 4.5mm air rifles are known for their high velocity and flat trajectory. The smaller pellet size reduces air resistance, making the pellets travel faster and on a more precise path. It is also important to understand that because 4.5mm pellets have a smaller diameter, there is less lead. This means the average weight is much lighter than that of a 5.5mm. The average 5.5mm is around 14 grains whereas the 4.5mm is 8 grains. This allows the pellet to generate high velocities much quicker than that of a 5.5mm. This feature is beneficial for shooters who are interested in target shooting or pest control at shorter distances. 
  
2. Less Drop: The 4.5mm pellets experience less drop over longer distances due to their flatter trajectory. This trajectory is helpful in terms of accuracy as there is less need to adjust the scope or drop lower on the reticle as you move further from your zeroing distance. This is a great advantage when teaching new shooters as it’s far less 
complicated to get a tight grouping. 
  
3. Power: A common misconception is more power is better. While this is true if you are trying to take down a big game, it does not ring true for all shooters. 4.5mm air rifles are known to have higher velocities but if you pay careful attention to the power (joules) of the rifle you will notice they are less powerful. This helps new shooters and children get more comfortable with a rifle, but it can also be a fun shooting experience. 
 
Disadvantages: 
 
1. Less Knockdown Power: The 4.5mm calibre is smaller in comparison to the 5.5mm, resulting in less energy being transferred upon impact. This would result in a problem with shooters dealing with larger pests or game animals. 
 
2. Wind Sensitivity: Although the flat trajectory is a plus, 4.5mm pellets are generally more sensitive to wind due to them being a smaller size and lighter. Shooters need to account for wind conditions more precisely when using this calibre. 
 
5.5mm Air Rifles 
 
Advantages: 
 
1. Increased knockdown power: The 5.5mm pellet is larger than the 4.5mm and so translates more kinetic energy upon impact. This makes the 5.5mm the perfect companion for hunting larger game or pests that require more stopping force. 5.5mm PCP air rifles usually allow the shooter to use very heavy slugs (bullet-shaped hollow point pellets) which are ideal for hunting. A 35-grain 5.5mm slug can take down large game and is a much cheaper alternative to firearms. 
 
2. Better Wind Performance: The larger pellets are less affected by wind compared to the smaller ones, resulting in improved accuracy in varying weather conditions. These pellets have more of a parabolic arch (upwards curve ending in a downwards curve) which allows them to travel with the wind instead of being blown around. 
 
3. Versatility: 5.5mm air rifles strike a balance between target shooting and hunting making them a versatile option for shooting enthusiasts interested in both activities. The extra power is also desirable for a lot of experienced shooters. 
 
Disadvantages: 
 
1. Slower Velocity: Due to the pellet being heavier, 5.5mm air rifles generally have lower velocities. Shooters will have to adjust their aim for longer distance targets more than that of 4.5mm. 
  
2. Because 5.5mm Air rifles are generally used for game they tend to be much more powerful, this does translate to a higher price bracket. If you are looking to buy a 5.5mm you will have to make sure you save a month or two longer. 
 
Selecting between the 4.5mm and 5.5mm air rifles all depends on your shooting preferences and intended use. If you are leaning more towards target shooting or small-pest control at shorter distances, the flat trajectory and higher velocity of a 4.5mm air rifle might suit you the best. On the other hand, if you’re a hunting enthusiast looking for more knockdown power to take down a larger game, a 5.5mm air rifle could be the better choice. It ultimately depends on what you’re looking for and what to achieve. Whether it’s precision accuracy, flatter trajectory, or greater stopping power, both 4.5mm and 5.5mm air rifles are great options.