December 8, 2020
We’ve all been conditioned to think that if a little bit of something is good, then more must be better! Well, when it comes to velocity in shotshells, it’s more of a law of diminishing returns and in reality, the phrase, “less is more” becomes a bit more fitting. Shotgunners tend to have this fallacy that faster is better and the muzzle velocity listed on the box is the same as the final velocity or “impact velocity” on their game. In short, it is absolutely not and that’s important for you to understand before loading up your gun. In this article, we’ll break down they key factors that affect your shotshell velocity and how they impact your final velocity from muzzle velocity.
First and foremost, the velocity printed on the box of shells is nowhere near the velocity that actually impacts your target. In fact, it’s at best half on impact depending on the type and size of shot that is used. All moving objects face air resistance. In fact, its Newton’s Third law summed up, for every action there is an equal and opposite reaction, and, in this case, it is dependent of a pellet moving in the air. The forces exerted on a moving object are directly dependent on the atmospheric conditions, size and speed. Since the drag or force induced on a sphere (pellet) is exponentially proportional to the initial velocity, the faster something is moving, the more resistance it faces. The following equation shows how to determine the drag, or “resistance” a pellet faces in air.
(D = Cd * .5 * rho * V^2 * A)
This equation simply states that the faster a pellet is shot (higher muzzle velocity) the faster or more aggressive it induces drag on the pellet. In short, since once the pellets leave the barrel, there is no force behind them pushing, and ultimately begins to slow down at an exponential rate. This is amplified on a faster pellet, than one shot at slower speeds. Furthermore, the “A” in that equation represents the area of a sphere in which that it reacts with the air of resistance. To compile both, the faster you try to throw a bigger pellet, the faster it slows down. Let’s look at the following chart (Figure 1) to explain.
As you can see, for every 100 fps extra in muzzle velocity, the impact speed does not lead to linear proportional increases at higher velocities. At 1550 fps, the difference in impact velocity as compared to 1450 fps is 28fps. However, when 1550 fps is compared to 1650 fps, the difference is 24 fps, and a total of 53 fps from 1650 to 1450. The faster the pellet is shot, the faster it will shed speed as it impacts the target. As its only needed 1.50” of penetration needed to consistently harvest ducks, the only thing you are gaining in excessive speed is added recoil and a marginal increase in lead time. In fact, the “time to target”, is only a mere 100th of a second faster on target. Given the assumption a duck is moving at 70 feet/second or 47mph at its fastest case, the increased lead time gained is only about a half of a foot. Faster pellets result in slightly shorter lead times, heavier pellets retain energy, shed less velocity and penetrate deeper (Figure 2). Then becomes the tradeoff for pellet sizes and pellet counts.
As mentioned earlier, the faster you shoot a pellet or sphere, the more air resistance is imparted. With an increased force from shooting a higher velocity, not to mention disproportional or inconsistent shot sizes/shapes, the increase for “fliers” or stray pellets is a guarantee. As the payload travels down the barrel and through the choke, all the forces on these pellets effect your pattern. As these pellets interact with each other, they either impart the force on each other through vibration, or absorb the impact through deformation. Anytime a pellet receives a force from another, it results in a negative response that either creates inconsistent pellet shapes or more stray pellets in your pattern. Bluntly put, the faster a payload is shot, the more inconsistent your pattern becomes.
With velocity, more often than not the tradeoff is a subsequent loss in your pattern retention. If pellet becomes a “flier,” its chances only increase by using more force from added velocities. Adding to that factor even more is if you have other uncontrollable variables such as inconsistent pellet shapes from the manufacturing process, or soft metals like lead, bismuth, or softer tungsten alloys which deform under setback. These irregular shapes and impurities create increased and variable resistances as compared to perfectly round spheres. The result is a larger air resistance factor from the drag due to how the air flow interacts with pellet. The smoother the surface, the more streamline the airflow is. The more inconsistent, the air at the molecular level interacts with a bit of “turbulence” which creates more hinderance in flight. This result generates more, “fliers”, inconsistent patterns, increased flight time from firing to impact and ultimately your final velocity and penetration. The more things change or have the ability to change in a shotshell pellet, the harder it is to consistently stay on target.
Since a pellet’s ballistic coefficient plays such a critical factor in velocity, which is derived from the pellet shape, a crucial factor in that end result comes from its ability to interact with the air resistance. Dense metals such as TSS have a hardness that eliminates its ability to be deformed under setback, or the initial forces under firing. As previously mentioned with respect to how less smooth and irregular pellets create drag, a ballistic coefficient takes into account a pellet’s form factor. A perfectly round spherical pellet has the ballistic coefficient that matches its sectional density. Materials such as lead, bismuth, and certain softer tungsten alloys often deform on setback creating a “form factor.” This form factor is an index to the overall shape of that pellet. The larger the deformation the higher the ballistic coefficient. The more deformed or uneven a pellet shape is, the harder it is to overcome the drag from wind resistance. This results in large losses of velocity from muzzle to impact.
As each individual pellet is shaped from manufacturing or deforms differently under setback, a pellet’s form factor is impossible to consistently calculate and reliably factor into ballistics software for modeling. In most cases, these pellets use empirical data from previous testing to best average the effects in software modeling. The following chart breaks down the most common shot sizes and their respective muzzle velocities, and how they translate to velocity, energy, energy density and penetration at target (Figure 3).
With these factors of density, pellet size, hardness/shape, and muzzle velocity being the main factors in impact velocity performance, it’s important to understand the compromises faced. Reducing a pellets size greatly cuts its wind resistance effects, but its tradeoff is often a result of a lack of mass resulting in lost velocity and energy. To circumvent, increasing a pellet’s density increases its mass and thus energy, energy density, and impact velocity. Increasing a pellets size maintains speed and energy, but the loss in pellet count reduces the ability to put “mass over target.” Illustrated above, the ballistics chart using the principles mentioned earlier in this article showcase that indeed, small, ultra-dense, and uniform pellets outperform a larger, much less dense pellet. The ability to increase density, maintain a perfect sphere and greatly reduce the surface area result in higher impact velocities, reduced lead times, and more pellets on target to achieve the greatest energy density and penetration possible on target.