Ballistics
Ballistics
Ammo Performance
The author has found that each pellet product has a measurable performance trend and has developed a programmable table which allows its downrange performance to be compared to any other tested pellet.
By Michael Whitworth
My wife tells me I missed my calling and that I was born to be a researcher or analyst. As long as I am free to choose the subject of the study I can agree with her observation. I love shooting, and I test and experiment continuously. I can spend hours happily mulling over recorded results of a shooting session.
In the field of air guns I have researched several aspects related to pellet performance which will be shared here. Many air gun manufacturers rate the velocity of the products they offer with the new lightweight alloy pellets. Like most consumers, I like the idea of a sizzling fast pellet streaking toward a targeted pest and knocking it over with impressive force. However, I wanted to know and not suppose how fast a pellet exited the muzzle of my gun and how it compared to other pellets. A chronograph gave me the ability to do that. Then I wondered how well each pellet carried its velocity downrange. After all, the first horse out of the gate is not declared the winner unless it maintains that advantage to the finish line. The velocities of the alloy lightweights may leave the traditional lead pellets far behind at the muzzle but do they carry that advantage downrange? What about pellet energy? Do these fast bad boys pack a punch? What about that .177 caliber screamer? Does it surpass the knockdown energy of the much slower .22?
I stocked up on an assortment of ammo and set up my chronograph to measure the velocity of each pellet product at the muzzle, and again at 20 yards. I did this with each pellet from at least 5 different air rifles or pistols firing 10 shot strings at each distance. By the time all the pellets had been tested, 15 different air guns were used to determine pellet performance. Things got interesting when I observed that every pellet product had a trend to behave a certain way downrange regardless of which rifle or pistol it was fired from. It may leave the muzzle at 700 fps from one gun and 400 fps from another but it slowed at nearly identical ratios from each gun. I had accumulated a lot of paper records for each pellet and from that began to predict the 20 yard velocity of that pellet after observing the muzzle velocity from a new test gun. I knew I was on to something when those predictions were consistently confirmed by the chronograph readings at that distance.
Because of this trend, I found that a numerical "performance factor" could be assigned for each pellet based on the chronograph records. I then determined to develop tables of pellet performance on my computer. This evolved into using Microsoft Excel where I substituted proven ballistic formulas into the table's formula program. Now all I need to do is enter the identity and physical characteristics of any pellet into the appropriate column, then enter the muzzle velocity and performance factor and the program calculates all the comparative statistics I want to know and displays them under the headings which identify the information. (Click here to access the tables.)
The performance factor is not the ballistic coefficient. It is simply a number which when divided into the velocity at a given distance will calculate what the velocity will be 10 yards farther downrange. Thus if the muzzle velocity is 800 fps and the performance factor has been previously measured at 1.054, the 10 yard velocity will be 759 fps and each successive 10 yard velocity can be determined by the program. I set up the tables to calculate these statistics all the way out to 100 yards since some gun and pellet combinations are perfectly capable to deliver consistent target or hunting accuracy at this range under favorable weather conditions.
With this functioning downrange performance table completed, at this point in my research some obvious facts about different pellet products, weights, forms and composition could be determined. For instance, the much higher muzzle velocities of some alloy pellets offered no advantage by the time the pellet reached practical hunting range. In several cases it was actually less than the heavier, slower-starting lead competitor. Why spend 10 times as much for a pellet that offers no practical advantage in a hunting context? I have almost no concern for how fast my pellets punch holes in paper at 10 yards. That is just the velocity side of the discussion. When you consider energy delivered at the target, there is overwhelming evidence in favor of the heavier pellets with the observation that heavy for caliber pellets also will fall behind the traditional weight pellets after about 40 yards. The tables tell the story on the pellets I have tested thus far.
There are several columns in the tables related to the measure of energy. First there is Kinetic energy, which is the most commonly used measure in advertising the power of a gun or projectile. Many experts do not consider kinetic energy to give a complete picture of hunting effectiveness. Obviously, you must first prove the pellet you are considering will deliver a consistent and desirably small group to the aiming point from your gun. I do not give any accuracy comparisons here for the reason that I found that one particular pellet and gun combination would produce very good accuracy, while the same pellet in another gun was lousy. I even observed this from one pellet product fired in two rifles of identical make and model.
Beyond the issue of accuracy, consideration must be given to the pellet's ability to penetrate into the vitals. I absolutely loved the performance of one somewhat light lead round nose pellet in my Crosman 2200 Magnum. It had good velocity, great accuracy, and the best performance factor of any tested pellet. Yet it proved to be a poor performer when it encountered the hide of squirrels. I switched to a heavier, slower pointed pellet and was pleased with quick kills. This brings me back to the earlier statement that many very experienced hunters do not embrace kinetic energy as the measure of killing effectiveness.
John "Pondoro" Taylor was a renowned elephant hunter having killed over 1,000 elephants. His experiences led him to develop "Taylor's Knockout Value" or "TKO". I have included a column in the table using his formula applied to our diminutive projectiles for those of you who might consider hunting elephants with a pellet gun. Well, really it is just to provide a different perspective to the energy comparisons. (Taylor himself was ridiculed for some of the light caliber rifles he used on elephants but I think he would have declined to face one with a Crosman 760 Powermaster.)
As much of a stretch as it may be to apply TKO to pellet guns, I do lean toward a formula that is not so biased toward high velocities in calculating energies. I have attempted to reconcile the two opposing perspectives with the column headed as "WLV". In addition to accounting for both viewpoints, this formula has been crafted to yield a value which is equivalent to the weight of an animal which can be cleanly and humanely killed at a given distance determined by the energy level the pellet delivers at that distance. However, this is developed from personal experience and not indisputable fact. I made an attempt to take into account pellet form (i.e. pointed vs. flat nosed) that may effect penetration. The kill weights listed may seem light to many readers but purposely favor humane considerations rather than technical possibilities. In other words, there is a very high likelihood of a clean kill with one well placed shot. I know you can kill a 12 – 15 lb. raccoon at 20 yards with a Benjamin NP XL-1100 but it isn't going to be a consistent first shot event with a winter coat and layered fat to penetrate.
For what it is worth, these tables reveal the findings of my thus far limited research and analysis of the results. More importantly it provides a program allowing the measurement and reporting of any projectile's downrange performance from any air gun. So, if your favorite is not listed, with a few initial velocity readings it can be plugged in to the table and compared to other options. To include in the tables every pellet made would take perhaps years and more cash than I can spare. The starting selection here at least seems to indicate the following:
• Some of the best alloy pellets have the velocity advantage to perhaps 40 yards but never carry as much energy as a slower lead pellet to the 10 yard line.
• Heavy for caliber pellets work better than the kinetic energy values suggest but at 40 yards or more offer no advantage to the standard mid-weight pellets.
• Accuracy is the first concern when choosing a pellet. Verify that you gun will shoot consistently with a pellet before purchasing any pellet in quantity.
• Penetration is essential to a pellet used for hunting larger or tougher prey. Light pellets do not penetrate fur and hide as well as mid-weight or heavy pellets. Heavier pointed pellets slip through furred prey better than other types.
• Pellets expand very little to not at all in hunting. Small caliber pellets, no matter how fast, do not equal the energy transfer of heavier, larger calibers. If your prey is larger than 4 pounds you need something larger than a .177 caliber even with a fast rifle and the best heavy pellet in that caliber. For squirrels you are fine to about 20 yards with a good rifle shooting a standard 7.9g pointed pellet at 700fps muzzle velocity. For prey over 10 pounds you should have something more than a .22 caliber for reliable one shot kills at likely hunting ranges.
I spent a good deal of time and money on the thousands of pellets sent downrange and a new chronograph following an errant downrange shot late in the testing. (It took a lot longer than feared for that to occur as I had already purchased a spare.) Perhaps this will give you some insight to guide you in your pellet selections and enable you to avoid misspent dollars on a pellet that doesn't fit you needs as well as another one.
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