Understanding Airgun Terminal Ballistics Part 1

By Jim Baumann

Author Air Rifle Ballistics

Copyright © 2000 Jim Baumann & Lame Rabbit Software

Many years ago, when the FWB 124 became popular, I bought one, and I was amazed at its velocity and power. This thing would push a 177 caliber 8.39 grain Beeman Silver Jet pellet out of its muzzle at 770 feet per-second, and that, fellow airgunners, was serious muzzle velocity for a 177 caliber airgun, in those days. This power level is under the current 12 foot pound UK limit. In fact, it is, just a hair over 11 foot pounds of power.

With such a super powered magnum airgun; I was sure that all the rats, pigeons, and rabbits would fall instantly dead, when shot with this high velocity wonder. Well, it killed the rats pretty quickly, when I placed my shots where I was suppose to; but, the pigeons were not dropping like they should. Most of the time, they would fall dead; but, sometimes they would fall and then just get up and stroll away. I could not understand it. The story I read in the Beeman catalogue said the Silver Jets went through the pigeons like a ripsaw.

While, most experienced hunters, already know the reason why I was having this problem. I am sure that even the most experienced of you will find these tests interesting. I have geared most of this to being under the UK's 12 foot pound power limit; you may also find that our higher powered airguns; don't always have that big of an advantage.

Anyway, I had run into this problem before, and I was at a bit of a loss; as to what could possibly be holding these dead pigeons up. I had the same problem when hunting Woodchucks with a 22 rimfire. If I did not shoot the chuck in the head; the darn thing would fall down and then run into his hole, (den), before I could chamber another round. Now, a 22 longrifle rimfire cartridge fires a 40 grain 22 caliber bullet at almost 1300 feet per-second, with a hundred and forty foot pounds of energy. Of course, they make much faster 22 caliber rimfire cartridges, now; but, that is another story. Our Woodchuck probably only weighed 10 pounds.

While woodchucks may have little to do with practical airgun hunting; there is a reason that I mention them, and that has to do with "terminal Ballistics". Gun writers have coined terms like "killing power" and "knock down power." Ballistics "Experts," will say that all of these terms are incorrect, and that's putting it in a nice way! I have already gotten into lots of trouble, with these so called "Experts;" Most, people use words that have, meaning to them, and that is all that matters. While the term "killing power" really can not be explained; "knock down power" can be. The idea is that when a game animal is shot the force of the impact literally knocks the animal down. This really does not make a lot of sense, when we talk about big game hunting; but, when we talk about small stuff, and airgun pellets; it just might apply.

Foot pounds of energy has little to do with the force needed to kill, a rabbit, or a rat. This value is subjective at best, and energy in foot pounds is really only good for comparing the energy output of one firearm cartridge to another, or, in our case, one pellet to another.

What I am referring to, with these terms is what actually happens when our airgun pellet strikes its target. The energy that is transferred to the target, or our game animal, be it varmint,(vermin), or dinner, or a pigeon that was defecating, on my clothes line.

Splattology

Shooting at different materials with airgun pellets is commonly referred to, in the USA, anyway, as Splattology. A very good term; as most use materials that are way to hard; giving real meaning to the word SPLAT, in Splattology. A long time ago, I used a concrete block as a back stop, and boy did those pellets splatter.....

This is all well and good; but, it really does not show us what happens when our pellet hits an animal; be it mouse, feral pigeon or rabbit. A concrete block, or an old phone book is hardly like shooting a game animal.

At that time, I had read about the over penetration of 177 caliber pellets; so, I went looking for a material that might give me some idea of what was happening when my pellets actually hit the game. Ballistics Putty, was way too hard, and a bit on the high priced side; besides, I would have to wait while it was being shipped.

I eventually found some Plumbers Putty, and began testing different pellets. The neat thing about this putty was that it showed the shock wave, or how the actual force of the pellet striking the target works. All of the pellets made very large entrance holes, and the holes kept getting smaller until the pellet, finally stopped inside the putty. It came as no surprise, that the flat and blunt nosed pellets made the largest entrance holes, and penetrated the least. All pellets left funnel shaped holes in the putty, with the largest part of the hole being the entrance area. This makes sense; because, this is the point at which the pellet still has most of its energy.

Since the Plumbers Putty shows the differences in pellet performance, I have repeated and expanded on those old test for you here. I did some compensating for the velocity loss; since I have never had a pigeon, or any other critter sit on the end of my barrel, of my airgun. Besides, I think that you would find the below 12 foot pound info more interesting. I started out with some 177 caliber pellets, and then they went directly to a few of the 22 caliber pellets. Please note, how much penetration happens with the 22 caliber pellets, in spite of there really low velocity, and small energy values. This is low energy, in foot pounds, even by UK standards.

One of the problems with terminal ballistics, and airgun pellets is that unlike bullets they lose there velocity very fast. So, compensating for this may make the information seem confusing. The "At ## yards" is based on the approximate distance the pellet would be from the muzzle at that velocity. In other words I used my ballistics program to calculate the remaining velocity, and the actual ballistic values from the tests that I have conducted, to find the approximate range that the pellet would be at, when fired from a 12 foot pound gun. For an example lets look at the first pellet. The 177 caliber 7.9 grain Crosman Premier. If our muzzle velocity is just under 800 feet per-second, our velocity at 30 yards would be about, 680 feet per-second, giving us 8.11 foot pounds of terminal energy. The "entrance hole" and "penetration" are the results of the pellet's effect on the putty, at the target velocity. While all of this is based on less than 12 foot pound of muzzle energy; I did throw in one 20 foot pound example.

The picture above shows the impact hole made in the plumers putty by a Beeman Kodiak pellet, traveling at almost 900 feet per-second.

PELLETS: 177 CALIBER:

Crosman Premier: Velocity At 30 yards 680 FPS; and Energy 8.11 Foot Pounds; entrance hole 7/8"; penetration 2 and 7/8 inches.

Crosman Premier: Velocity At 50 yards 590 FPS; and Energy 6.10 Foot Pounds; entrance hole 5/8"; penetration 2 and 3/8 inches.

Beeman Silver Jet: Velocity At 20 yards 661 FPS; and Energy 8.14 Foot Pounds; entrance hole 7/8"; penetration 2 and 3/4 inch.

Bisley Super Field: Velocity At 25 yards 651 FPS; and Energy 7.98 Foot Pounds; entrance hole 3/4"; penetration 2 and 3/4 inches.

Beeman Silver Bear: Velocity At 12 yards 693 FPS; and Energy 7.57 Foot Pounds; entrance hole 1 and 1/8"; penetration 2 inches.

Beeman Silver Bear: Velocity At 30 yards 570 FPS; and Energy 5.11 Foot Pounds; entrance hole 5/8"; penetration 1 and 3/4 inches.

Beeman Crow Magnum: Velocity At 29 yards 540 FPS; and Energy 5.69 Foot Pounds; entrance hole 1/2"; penetration 1 and 1/2 inches.

Beeman Silver Bear loaded backwards: Velocity 680 FPS At muzzle. entrance hole 1 1/8"; Penetration 1 and 3/8 inches.

Beeman Kodiak, AKA Bisley Magnum: Velocity At 35 yards 598 FPS; Energy 8.42 Foot Pounds; entrance hole just under an 1"; penetration 3 and 1/4 inches.

Beeman Kodiak, AKA Bisley Magnum: Velocity At 50 yards 550 FPS; Energy 7.25 Foot Pounds; entrance hole 11/16"; penetration 2 and 7/8 inches.

Beeman Kodiak, AKA Bisley Magnum: Velocity At Muzzle 900 FPS; Energy 19.06 Foot Pounds; entrance hole 1 and 1/2 inches; penetration 4 inches.

22 CALIBER:

Crosman Premier: Velocity at Well over 50 yards 356 FPS; Energy 4.02 Foot Pounds; entrance hole 5/8"; penetration 2 and 1/2 inches.

H&N Match: Velocity At 50 yards 364 FPS; Energy 4.04 Foot Pounds; entrance hole 5/8"; penetration 2 inches.

Crosman Copperhead Pointed: Velocity at well over 50 yards 357 FPS; Energy 4.09 Foot Pounds; entrance hole Just over 1/2"; penetration 2 and 1/8 inches.

Gamo Magnum, (pointed): Velocity at or over 50 yards 342 FPS; Energy 4.10 Foot Pounds; entrance hole just under 1/2"; penetration 2 and 1/4 inches.

Special Note:

Plumbers Putty is not supposed to dry out; but, I have found otherwise. It will, if left to the elements after a length of time. It will also change consistency with temperature, and humidity. And last, but not least, it does seem to vary in consistency, from batch to batch; so, if you chose to test with this stuff; keep all of this in mind, and don't do a comparison 6 months later, particularly when the temperature might be 30 or 40 degrees hotter or colder.

I hope you noticed the backwards Silver Bear. I did that just for fun, and while there was some pellet expansion in the putty, this backwards pellet expanded to almost 9 millimeter. However, shooting it front wards, on gave an expansion to only 20 caliber at almost 700 feet per-second. However, this expansion disappeared when the velocity dropped to 570 feet pre-second.

The Crow Magnum expanded to .235 when hitting the putty at 540 feet per- second. This was the only pellet were the expansion was real noticeable.

The only none hollow point pellet that appeared to expand was the Beeman Kodiak AKA Bisley Magnum, and according to my micrometer it went to 19 caliber; but, this only occurred when the pellet was going at 900 feet per-second. At 600 feet per-second, no expansion was noticeable, by my micrometer. The Kodiak only penetrated 3/4 of an inch deeper into the putty at 900 feet per-second and the pellets entrance hole, or impact point was a bit bigger. But, from a practical perspective there did not seem to be that much of a difference, between the pellet going 900 feet per-second and the same one going only 593 feet per-second! Go figure!

This was all well and good, I thought; but, this does not seem very much like a game animal, and it was most surely nothing like shooting a pigeon. I decided that I needed to find something that might resemble animals in some fashion. There was only one material that I could come up with that would have consistency, and be something like an animal. It is something we are all made of, and that's water. Of course, animals have fur, or feathers, and bones and so on; but, still most of the body is made of water.

While, it sounds too simple, and it is; it is still a good place to start. Since water won't sit still; I needed a container. I found that those thin plastic milk, and water jugs to be ideal. I was amazed that all of the pellets shot out of my FWB went right through both sides of the jug, and through the 6 inches of water. These were gallon jugs, and a gallon of water weights over 8 pounds. This was certainly more than a feral pigeon, and while the jug was rather soft; I was still surprised that all the pellets went through it. I did notice that the flat nosed pellets did punch a much more well defined hole in the jug, just like they do on paper targets. In fact, the pointed pellets seemed to leave a smaller hole that their actual diameter.

I have, again, repeated these tests for you, and even all of the low velocity 22 caliber pellets penetrated all the way through the filled water jug. Again, even the flat nosed 22 caliber H&N Match with a velocity of only 364 feet per-second and only 4.04 foot pounds of energy, it went through the 6 inches of water and both sides of the jug. This surprised me, and I had to do it more than once to satisfy myself that it was true.

The Beeman Crow Magnum pellets went through both sides of the jug, and the water, even at 540 feet per-second. The odd part, about the Crow Magnum pellets and the water jug; was the lack of expansion on the part of these pellets. They did great on the putty test; but, very little happened when they hit the water jug.

The Silver Bear, would not go completely through the jug, when the velocity was dropped to 570 feet per-second; but it did dent or punch a tiny hole in the back side of the water jug. The Silver bear seemed to want to exit the jug at an angle; but, this was not always the case, and it is nothing more than an observation on my part.

With the 22 caliber holes the water poured quickly out of the jug, and there seemed to be little difference in the size of the holes that the 22 caliber pellets made both, when entering the jug, and when they exited out the other side. I suspected that this over penetration may not be limited to airgun pellets; but, to sub sonic, and/or slow moving bullets.

With that in mind, I decided to up the power a bit; so, I dug out one of my 22 rimfire rifles, and repeated the water jug test with a CB Cap. The CB Cap fires a 29 grain 22 caliber bullet at 700 feet per-second, gives an energy value of over 32 foot pounds. Well, this split open the water jug; but, the actual exit hole was no larger than the entrance hole.

This shows the holes made by airgun pellets. The left jug, was shot by the 22 caliber H&N match and a 22 caliber Crosman Premier. Can you see any difference in the two holes? The jug on the right was shot by a 177 caliber Beeman Silver Set, and a 177 caliber Beeman Silver Bear. The tiny stream in the back of the jug, ( right side), is from the exit hole of the Pointed Silver Jet. The larger and some what Ragged hole in the back of the jug was made by the Silver Bear Exiting the jug.

The Silver Bear, would not go completely through the jug, when the velocity was dropped to 570 feet per-second; but it did dent or punch a tiny hole in the back side of the water jug. The Silver bear seemed to want to exit the jug at an angle; but, this was not always the case, and it is nothing more than an observation on my part.

With the 22 caliber holes the water poured quickly out of the jug, and there seemed to be little difference in the size of the holes that the 22 caliber pellets made both, when entering the jug, and when they exited out the other side. I suspected that this over penetration may not be limited to airgun pellets; but, to sub sonic, and/or slow moving bullets.

With that in mind, I decided to up the power a bit; so, I dug out one of my 22 rimfire rifles, and repeated the water jug test with a CB Cap. The CB Cap fires a 29 grain 22 caliber bullet at 700 feet per-second, gives an energy value of over 32 foot pounds. Well, this split open the water jug; but, the actual exit hole was no larger than the entrance hole.

"Well, now what," I thought, and the only thing to do was up the power again. Maybe, the low velocity kept the lead bullet from expanding. Well, I dug through my box and came up with a box of CCI Green Tag. This is target ammo, and it gives a muzzle velocity of about 1150 feet per-second, with about a 100 foot Pounds of muzzle energy. That's just a bit over the UK limit; but, lets see what happens.

This shows the shock wave from the impact of a hundred foot pounds of energy; but, it also shows the the actual exit hole is still only 22 caliber

Well, the cap came flying off the jug and the back of the jug split open, and all the water gushed out. It looked real impressive; but, on closer examination the exit hole was only 22 caliber. Now, wait a minute here, tell me that it isn't so! I had to try something else. I had to see if this bullet was really not expanding in our water and jug medium. My wife had tossed a rather heavy laundry soap jug in the recycle bin; so, I grabbed it a filled it with water. This time I left the cap off the jug and unleashed a hundred foot-pounds of energy on and into this water filled gallon jug. This laundry jug was just a bit thicker and seemed a lot tougher than the Milk/Water jugs; but it also contained 5 and 1/2 inches of water, thickness wise.

Some water splashed out of the top; but, even though it was sitting on my rickety folding stool, the jug hardly moved. The picture below shows the exit hole, from the inside of the jug. I cut the jug apart, to show you the exit hole, and the bullet, next to the exit hole, is one of the CCI Green Tags that I used in this test.

This shows the exit hole, made by the CCI bullet after punching through the thicker plastic jug and 5 and a 1/2 inches of water, and the CCI rimfire bullet used to make it.

The whole point here, is that the exit hole was no bigger than the entrance hole; and if that is not enough; the exit hole was no bigger that of the 22 caliber airgun pellets, fired with only 4 foot pounds of energy. The only difference between them was the thickness of the plastic that the different jugs were made of. I did not try to see if the 4 foot pound 22 caliber pellets would go through the laundry jug, and they probably would not go through both sides; but, they went through the same amount of water like the proverbial knife through hot butter.

The exit hole made by the CCI Green Tag, for all its energy, did about the same thing. It only punched a 22 caliber hole through our test jug. The fact of the matter is that sub sonic pellets, and bullets expand little, if at all when striking game. I remember the first Gray Squirrel that I ever shot; I hit it squarely in the chest from about 20 yards, with a 22 longrifle bullet. The Gray did not move, and then he turned and a started up the tree. He did not get more than a few feet, before he fell dead; but, even though he was hit with about 120 foot pounds of energy; it did not knock him down. Close examination of the Squirrel revealed that the bullet had indeed hit him just to the left of the center of his chest. The exit wound was just to the right of his back bone. The bullet had passed through his body with out dissipating much of its energy.

This was part of the problem I had with the wood chucks; the bullets were going through with out expanding, and not doing enough damage to keep the chuck from reaching its den, never to be seen again. The long and short of this story, is that I went from a 22 longrifle to a 22 Rimfire Magnum, which turned out to be a bit iffy at ranges over a 100 yards. From there I went to a 22 Hornet, with a muzzle velocity of 2690, and developing 739 foot pounds of energy. This may sound like over kill, and it is; but only if you shoot them in the head; but, otherwise it is not, and I have lost a couple of Chucks shooting them through the chest with the Hornet; but, very, very few.

The reason that I have mentioned the Woodchucks; is that a lot of airgunners over here hunt them. I have killed a few with a 177 caliber air rifle; but, only with head shots, and only when I have been sure of the shot. If you want to shoot them in the chest; use a 9MM Career 707.

While our gallon jug might resemble a wood chuck in at least size and weight, what about a rat or a squirrel? How about one of those garden raiding chipmunks. I don't know about you but I have never shot any of those that weighed 8 plus pounds. Or even the 5 pounds that our block of plumbers putty weighed, and lets face it, our targets aren't flat like the water jugs, or the plumbers putty. At this point I had more questions than answers! How much of our pellets energy is spent on our intended target; if our pellet just punches through it. These are things we will look at, in part 2 of Understanding Terminal Ballistics, or more Splattology than you ever wanted to think about.