1 About this module

• Prerequisites:
• Objectives: This module compares heavy and light pellets, given everything else is the same.

2 The Hype

The hype of lighter pellets is that they can go faster compared to heavier pellets. In other words, light pellets are speed demons.

3 Why is faster better?

Technically, faster is better because the trajectory is flatter. There is drop to account for. This is more significant for targets that are far away. The drop of a pellet is a function of time, $D=\frac{a{t}^2}{2}$. In our case, $a$ is the acceleration or gravity, it is about 10 meters per second squared. $t$ is the time of flight of a pellet, and $D$ is the amount of vertical drop due to gravity.

A faster pellet means it gets to the target faster, which reduces $t$. As $t$ decreases, so does $D$.

A smaller drop is important for sighting systems that cannot account for elevation change.

4 How much faster?

Given that a barrel transfers the same amount of energy to pellets regardless of their mass, $E=m{v}^2$, where $E$ is the energy (often measured in foot-pount in the U.S., Newtons elsewhere), $m$ is the mass (grains in the U.S., grams elsewhere) and $v$ is the velocity (feet per second in the U.S., meters per second elsewhere).

If $m$ is halved, then $v$ has to increase by $1-\sqrt{2}$. This turns out to be about 0.4, or 40%. If you have a set up that launches a 10-grain pellet at 500fps, then a 5-grain pellet from the same set up will be launched at about 700fps.

If a light pellet is launched in vacuum with 100% energy conservation, then the time of flight is $\frac{1}{\sqrt{2}}$ of a pellet twice its mass. This turns out to be about 30% less drop. When it is all said and done, the actual vertical drop is half of that of a pellet twice as heavy/massive.

5 Reality check

5.1 Energy conservation

Our calculation was based on 100% energy conservation. A set up transfers the same amount of energy to pellets of different masses. This is, unfortunately, not true.

Some energy is lost in the process regardless of the mass of a pellet. This includes friction between a pellet and the barrel, air resistance and many other factors. Let’s take a look at an emperical data point.

An IZH46M launches a JSR Exact Heavy pellet (about 10 grains) at 420fps. The same pistol launches a Crossman lead-free hollow point pellet (about 4 grains) at 560fps. Using $E=m{v}^2$, we can see that the heavier pellet has $10\cdot 420^2$ units of energy, while the lighter pellet only has $4\cdot 560^2$ units of energy.

While the increased speed makes up for some difference due to the mass, there is still a 30% net loss of energy.

5.2 Ballistic Coefficient

BC is a constant used to compute the trajectory of a projectile. Even if two pellets have the exact same shape, the heavier one has a more favorable BC. A better BC means that a pellet does not get as much drag as a function of distance traveled.

The bottomline of a better BC (higher value) is that the speed of a pellet does not decrease as much as a pellet that has a worse BC (lower value).

Think of it this way, we are putting the same amount of energy launching a ball of lead and a ball made of styrofoam. The lead ball goes slower, but its speed does not change much. The styrofoam ball goes very fast, but it also slows down very rapidly.

Because of BC, a lighter pellet may take longer to reach a far target than a heavier pellet. In addition, wind also has more effect on a lighter pellet than on a heavier pellet. Assuming the force $F$ acting on a pellet is constant, the drift distance is $D=\left(F∕m\right)t^2$. $m$ is the mass of a pellet. This means that a pellet twice as heavy get half the drift distance due to wind.

Of course, $F$ is not a constant in this case. As a pellet matches the speed of wind, $F$ decreases.

6 What is the bottomline?

Heavier pellets can be troublesome for sights that cannot account for elevation changes. Other than that, however, heavier pellets are more accurate, loss prone to wind factors, and they deliver more energy on to the target.

Lighter pellets are better for short range indoor targets where energy delivery is not important.

7 Using heavy pellets and an iron sight

Some pistols, such as the IZH46M, are not friendly to scopes that has mil-dots for on-the-fly elevation adjustments. As a result, these pistols cannot easily account for the drop of a heavy pellet over longer distances.

While this makes an iron sight harder to use, it is not impossible.

The most important part is to record elevation settings with precision. The use of a caliper is important. After sighting in at a distance using a particular pellet, measure and record the elevation setting. Depending on your sight, the measurements may be done in different ways.

If you are lucky enough to have clicking adjustment, one way is to record the number of clicks from one end of the adjustment range. This can prove to be cumbersome for people who cannot count straight. Nonetheless, this method does not require the use of a caliper in the field. You can write down a list of clicks for common distances and use that in the field.

The last method is just to rely on experience. An iron sight can aim high or low. Instead of making the top of the front blade level with the top of the rear sight, you can intentionally offset the top of the front blade above or below the top of the rear sight blade. In this case, the amount of offset is difficult to mark or measure, you just have to develop a ”gut feeling” for the offset at different distances.

Remember the offset as a ratio of the height or width of the notch on the rear sight blade.