Energy transfer – some things you may not know

by B.B. Pelletier

Today’s topic was suggested by dsw. I’m going to explain energy transfer from a practical standpoint, then I will try to back up what I say with a few facts.

The question I’m answering is, “How does a pellet transfer energy to its target?” If that is different from what dsw asked, I apologize.

1. Energy is transfered as deformation and heat
When a moving lead pellet is stopped suddenly by a hard immovable surface, such as the steel back of a bullet trap, it deforms on the surface of the steel. Up to about 550-600 f.p.s., deformation is all you can see, but if you were to grab the pellet an instant after it stopped, it would be very hot, too. This heat is also part of the energy the moving pellet gave up when it suddenly stopped. If the pellet hits the steel faster than 550 f.p.s., small pieces of it break off and fly away, taking energy with them. At 700 f.p.s., some of the pieces are so small that we call them dust, and at 800 f.p.s., the heat from impact is so great that some of these pieces of dust are instantly melted. To the shooter, they appear to be sparks in the bullet trap.

2. Wound channels
Animals are softer than steel, so the pellet tends to punch through the tissue, destroying it as it goes. Here is what DOES NOT happen: A pellet has virtually zero hydrostatic shock, which is how modern small-caliber bullets kill game. To get that kind of tissue-destroying shock requires much more velocity than pellets can achieve. The wound channel of the fastest pellet rifle made (which I believe is the AirForce Condor in .177 caliber) WILL NOT be significantly larger than the diameter of the pellet.

3. Energy is transferred as impact
Impact energy is what moves the animal. It’s the same energy that less-than-lethal weapons, such as shot-bag launchers, use to knock down people without killing them. A pellet that remains inside an animal transfers all of its energy to the animal. If the pellet goes through the animal and out the other side, only a portion of the energy is transferred. If penetration is not deep, the impact energy will be greater (proportionally) than if the penetration is deep and more energy is used to cut through tissue.

Impact energy demonstrated
The buffalo hunters used large-caliber (.40 to .50) rifles and very heavy bullets (350-550 grains). The best buffalo guns would not only kill with one shot at 300-600 yards, they also often knocked down an 1,800-2,000 lb. animal! In contrast, when a .30 caliber (.30/06) high-velocity bullet is used on buffalo, it can take 2 to 10 shots to put the animal down. The .30/06 develops about 2,800 foot-pounds of muzzle energy, and a .45-120-550 Sharps (the rifle Matthew Quigley shot) develops about 2,400 foot-pounds, yet the larger, slower bullet kills faster and moves the animal (knocks it down) when it strikes. This is an ideal example of the optimum use of energy transfer.

I didn’t make up those facts about the .30/06 and buffalo. That was from a Denver Post story in the early 1950s, when the city thinned a local herd of buffs to feed the poor at Christmas. Only one animal out of eight was killed with a single shot.

4. Metallic Silhouettes
The problem of energy transfer came up early in the sport of metallic silhouettes. In this sport, you shoot at steel silhouettes of game animals at various distances. The ram is the largest, heaviest target and is placed at 500 yards. All the silhouettes have a flat foot that rests on a stand. To get credit for a hit, the silhouette must be knocked completely off the stand. Shooters have tried accurate calibers such as the .243. They find that, even though the rifle has the necessary energy at 500 yards, it often strikes the target wrong and only twists it sideways. A larger caliber will completely spin it off the stand. The energy the larger bullet is able to transfer to the silhouette is greater than the energy the smaller bullet can transfer.

Energy transfer depends on what the pellet hits, how fast it’s moving when it hits and what the pellet is made of. A pure lead pellet holds together well. A hard alloy pellet tends to break up earlier, and a synthetic pellet often separates in game. Once it does separate, however, the metallic core stays together.

What the pellet hits is extremely important. A freight train moving 10 mph has many millions of foot-pounds of energy. Yet it can hit a rabbit jumping across the tracks and not bruise him. But if it hits an automobile – look out!

5. How to improve energy transfer
Slow down the pellet! That usually means shooting heavier pellets, although some airguns also have power adjustments. Use an inefficient pellet nose shape. Wadcutters are very inefficient penetrators, as are hollowpoints, like the RWS Super-H-Point.

Energy transfer is important to the airgun hunter or pest control shooter. We work with such a small energy budget that we cannot afford to waste anything. Learn what it takes to get the most from your airgun.

33 thoughts on “Energy transfer – some things you may not know

  1. BB,

    Nice, very informative. I am sure there wi9ll be more to follow on this.

    My guess is that a springer with a rated muzzle velocity of 1000fps shooting a 10.6gr pellet will not have the energy at impact that a precharged pneumatic with he same pellet and rated muzzle velocity. Understanding of course the 10.6gr pellet will be traveling much slower than 1000fps in both guns.

    Infact, this this brings home your point on foot pounds at the muzzle being a better measurement.

    Anyway, how ever good or bad I may have worded my “theory”, am I right? Does a springer lose something at impact that the others don’t?

    Where’s the “Kinetic Energy Guy” when you need him? (ha ha)

    dsw


  2. dsw,

    Once the pellet leaves the barrel, it performs the same regardless of what launched it. 1,000 f.p.s. is 1,000 f.p.s. no matter where it comes from.

    Now, if a gun is RATED at 1,000 but only delivers 950, that is an entirely different matter.

    B.B.


  3. BB,

    I have been assuming that with the amount of air used by the precharged gun would cause the pellet from it to continue to accellerate.

    Thanks for the answers!

    dsw


  4. Oops, a common misconception about energy transfer.
    If the bullet had enough force to knock the shooter down, then it may knock someone of equal size down (engery is not created while the bullet travels!). Watch the video of someone getting shot with a vest on – they do not flinch more than the shooter – the energy at impact can not exceed the energy when it is released. Likewise, it is not possible to knock a large animal down – they may jump and trip and fall, but the force is not enough to push them down.


  5. Energy transfer,

    I don’t think I mentioned knocking the shooter down, did I? If so, I didn’t mean to. Of course the bullet can’t knock the shooter down because it isn’t directed at him, except in a suicide.

    As for knocking down game animals, let’s start with the shot bag. It does, indeed, knock a person down, as in off their feet, on their can on the ground. Now, whether that’s because it puts them off-balance enough that they continue to fall, like a punch from a prizefighter, I don’t know for certain, but shot bags will knock people down.

    As for game being knocked down, I’ve done it more than once. You might call it an instant kill, except the animal did not expire until many seconds later.

    Your protective vest example is interesting. I have seen protected people go down when the round was major, such as a .44 magnum, but I’ll admit I’ve also see men withstand a hit of a few hundred foot-pounds, such as from a 9x19mm. They did move, however, which is where at least some of the energy went. I’ve only seen recovered slugs from one type of vest – the type with ceramic plates behind.

    I don’t understand your statement, “-the energy at impact cannot exceed the energy when it is released.” Can you restate that?

    I have seen numerous videos of big game animals falling over sideways, opposite the direction of the shot. When they hit the ground, their feet continue up in the air as if they are rolling on the ground. That is what I am describing as being knocked down by a shot.

    In passing, I saw Jim Scoutten take several giant steps backwards about a month ago when he fired a large-bore elephant rifle on his TV show.

    B.B.



  6. Energy transfer guy,

    I guess I need to go to proof read school, sorry. What I should’ve said is “….pellet to continue to accelerate BREIFLY after leaving the barrel.

    I’m not sure that what you are saying about energy transfer is what you were thinking either.

    The shooter knows there’s a kick coming when he shoots. The target on the other hand is just peacefully eating grass, not prepared for the sudden “energy transfer realized.”

    I suppose if you accidently and unexpectedly shot whatever firearm would knock down a deer and you happened to hit the deer, then I guess you both would land on your whatevers.

    havin’ fun with ya!

    dsw


  7. Hey BB,

    Do you have a scale or formula for decrease of energy vs. distance for diobolo style pellets?

    I know I read something here somewhere on that, but don’t remember where.

    Thanks, ( I have a pesty raven around my house, thought I’d do some math before seriously trying to get him with my .177

    dsw )


  8. dsw,

    That new book I mentioned earlier this week has a great discussion of pellet velocity loss. Above the speed of sound, the velocity loss is tremendous. Between 800 f.p.s. and the sound barrier it is very high. Once the pellet slows to under 800 f.p.s., the velocity loss starts slowing down. And each pellet is different.

    Figure 60 percent of initial ENERGY remains at 50 yards. That’s conservative, but not very.

    I’ll try to come up with more accurate info, but I wouldn’t hold my breath!

    B.B.


  9. BB

    Thanks, I was figuring 75 percent loss.

    This is like finding money in the pocket of a coat that you haven’t worn for a while!

    The book is on the way.

    dsw





  10. Fascinating info you put out, BB ! How can I sign up to get your daily blog entries as emails ? or do I just have to keep looking on PyramydAir’s site each day ?

    Penetration and energy transfer … I have some H&N HP .22 pellets of 12.65 grains, and a slew of .177 BBs which sit nicely like a golf ball on a tee on top of the HPs with a dot of Super Glue, making a 17.75 grain combo (BB weight 5.1 according to PyrAir site) that is too long for the mag on my AA 410 (see below), but it is one of my ideas for a Talon or Condor I am considering (see below) … any thoughts from anyone as to killing effectiveness of such a hard-tipped round vs. a domed or pointed all-lead pellet of similar weight ?

    Also, an AirForce question … I am considering trading in my Air Arms S410 Xtra-Hi .22 for a rifle from Air Force … When I bought the 410, I was very turned off by the idea of single shot rifles … spoiled by M-16s and M-4s in the Army for 20 yrs, I guess … so I settled on a bolt-action 10-rd. rotary model … have learned the hard way about pellet length vs. magazine depth … spent a lot of time Dremeling down the cores of saboted Skenco pellets and the tips of JSB Predators I was lucky enuf to get free as samples from their mfr in Colorado after swapping several emails … nice guy … but I digress … sorry … I like the idea of quieter shooting with the Talon SS, but what I really want is killing power on larger game, which I think is only going to come with a Condor on hi power with heavy pellets like Eun Jin’s … like the SWAT police using them to take down drug dealers’ guard dogs … there are coyotes in my area who have already claimed one of my cats for their dinner and one of my neighbors’ cats too … so what I’d love to see is a comparison of ft-lbs with a Condor using the standard 24″ barrel vs. the same rifle with a 12″ barrel and SS end caps, same pellet and various power settings … I know there will be some loss of power, but how much ? Also, I’d like to hear from Talon / SS / Condor owners out there, how fast can u reload and get off a second accurate shot ? In a hunting / defensive scenario, if the first shot doesn’t kill the critter, having a second shot available in 2 seconds or less could mean a lot if the wounded and pissed off animal comes at you … I can do that with my 410, but I think a Condor would improve my chances considerably of the first round being all I need … or at least getting a knock-down while I insert the next round to finish the furball off b4 he has a chance to get his paws and teeth on me. Also, any rumors floating around that Air Force will add multi-shot mags to their products in the near future, maybe such as the Logun S-16, which I’d prefer over Condor if it could compete in the power dept. ?

    Thanks for reading, sorry this is s–o–o–o–o l—o—n—g LOL !!!!!!!

    Leon


  11. I know somebody is gonna say “oh no, not HIM again !” … but here’s another thought of mine about Air Force’s rifles … again, compared to a Logun S-16 … and my AA 410 XtraHi … nice to have an on-board air-remaining-gauge, which AF doesn’t seem to currently think is necessary … any rumors they are considering that feature in future models ?

    Leon


  12. Leon,

    Yes, a looooooong comment, but they are welcome here.

    Don’t look for a manometer (the gauge in the air tank) from AirForce. It compromises their DOT-certified tank, and most of us won’t live long enough for government re-certification.

    A Condor with a 12-inch barrel and the SS end cap was tested by AirForce. It’s 75 f.p.s. faster than an SS and about as loud as a Talon (the 18-inch barrel). In other words, not much of an improvement. I understand there is an AirForce dealer in Kansas who makes a frame extension for the Condor so the muzzle can be contained. It’s supposed to be quieter, if you can believe the forums – which I usually don’t.

    The Talon SS is used by some Eastern SWAT teams for drug bust guard dogs, so there is already enough power for what you want – short of coyotes. At close range, 25 foot pounds can be adequate for a brain shot, but it is definitely not sporting to hunt game of that size.

    As for your composite pellet idea, it’s been tried by a British company who is the laughingstock of the airgun world. If you want to see crazy pellets, try it!

    Thanks for the comments,

    B.B.



  13. shootin’ blanks,

    A muzzle brake (not break) is a device put on firearms to utilize the exiting gasses to reduce felt recoil. It is sometimes called a compensator.

    On airguns, most muzzle brakes do nothing, or else they are just an extension of the barrel for easier cocking.

    Silencers are a sensitive subject. They are controlled by ATF in this country. You can own one but you have to have a $200 tax stamp for it. Silencers can be built into airguns and some, like the TX 200, have them, but if they can be detached and mounted on a firearm, they require the tax stamp.

    B.B.





  14. Michael,

    You have a half-formed question. What do you want to know, or what are you looking for?

    What do you mean by “better?”

    B.B.


  15. I am looking for an air gun that can be used in the suburbs without having the police being called in and for squirrels. I was thinking the 2260 is better because of the foot-poundage.



  16. Michael,

    The Gamo Hunter would be better than either CO2 rifle because a spring gun is not as affected by low temperatures as a CO2 gun.

    A Benjamin 392 would also work, but the Gamo Hunter will be quieter.

    B.B.







  17. Reference to the guy with the coyote problem. Why not use a 9mm Career ultra, it’s a five shot repeater with about 130 pounds
    muzzle energy using 90 grain pellets. The only drawback is it’s noise, I know I’ve got one.



  18. B.B.–Scott298–I believe that using the .177 for hunting has to be limited to pelletts 10gr or higher to carry enough enetgy to the target and the shot placement has to be more critical as in a lung or heart shot. These will probably pass thru a squirrel but it will surley kill him. what really needs to be done is to hit him in the head or shoulders so the pellett doesn,t pass thru. I can see where the .22 you can be a little more liberal with your shot placement as you know the .22 is carrying more energyand will thus stay in the animal better but in both cases you still need proper shott placement. shooting a squirrel in the rump with a .22 will not kill him instantly and will still leave him with his front legs to get away and more than likely die a few hours later-so .177 or .22 I believe proper shot placement is still key. When it comes to high powered rifles like the 30.06 there is so much energy when the round enters the target it causes what ever organs it hits to explode and basically send it’s own body parts-like shrapnel thru other parts of the body-this is why hitting a buffalo with a 50 cal that is slow moving is like hitting him with a truck-the immediate force is transfered over a larger area while the 2300fps 30.06 passes quickly thru rhe animal taking out multiple body organs-the sharpnel effect-which gives the animal time to lumber on for some distance before it knows it’s hit-it happens too quickly-quess I just answered why .22 is better for hunting


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