Interesting ballistics

by B.B. Pelletier

Last week, we had a question about pellet drop, and a reader answered it correctly. The question, however, prompts me to post a few ballistic facts that may be of some interest to you.

Pellet drop
Galileo demonstrated the constant acceleration of gravity by dropping two different sized balls from the Leaning Tower of Pisa. Both hit the ground at the same time. When you shoot a pellet from a barrel whose bore is parallel to the ground and drop a pellet from the same height, both pellets should hit the ground at the same instant. The pellet that was shot, hits far away from you. How far depends on how fast it was traveling and how much it slowed down from the drag on its skirt.

What a drag!
Drag slows the pellet, and both weight and aerodynamic shape fight drag. Vertical drop is a constant. Therefore, light pellets hit the ground closer to the muzzle (at a given velocity) than heavier ones, assuming the same drag. I’m not saying that heavier pellets fall at a different rate than light ones, but that they take longer to slow down. Between two pellets of the same weight and aerodynamic efficiency, the slower one hits the ground closer to the muzzle.

HOWEVER – and this is the ENTIRE POINT I’m making – the “givens” listed above are NEVER the same, so trying to have a meaningful discussion about which pellet shoots farther or falls closer to the gun is pointless and futile! Instead, get out into the field to do the actual testing. That is the only way to find out what will really happen!

Mythbusters busted!
The popular TV show Mythbusters aired a segment on a “magic bullet” of ice that was supposed to kill someone when fired from a firearm, then melt without a trace. In that segment, they said that bullets don’t stop accelerating at the end of the barrel, and they ran a high-speed film clip showing gas blowing past a bullet as it exited the muzzle of a gun. Their premise sounds good, but it’s not correct. For all intents and purposes, and with the finest test equipment available, bullets stop accelerating when they leave the muzzle. I have done thousands of chronograph tests that show a gun has higher velocity at 12 inches from the muzzle than at 24 inches. I have tested both airguns and firearms this way and they work the same.

There MAY be a short region an inch or two from the muzzle where some slight amount of additional acceleration occurs, but the amount is both too small and the effect too brief to measure by any means I have access to. The high-speed gas blowing past the exiting bullet is rapidly losing its energy, which it has been doing since the bullet was about halfway down the barrel. It may act to destabilize the bullet slightly, but it doesn’t push it any faster. Having gotten that off my chest, I still enjoy the Mythbusters and find most of what they do very creative and accurate.

Precession will blow your mind!
Precession can be described as the tendency of the spin axis of a rotating body (a pellet in flight) to twist at right angles to any external force. Stated simply…when a spinning pellet encounters a force from the right side, it will climb if it’s spinning to the right or dive if it’s spinning to the left! The force will also move the entire pellet in the direction it is applied!

So, if your right-spinning pellet encounters wind from the right, it will move UP and to the LEFT. The UP movement will be smaller than the LEFT movement, especially since the pellet is also being pulled DOWN by gravity! Please explain all the other permutations of this phenomenon to yourself at this time.

Confused? You’re not alone. This phenomenon is quite confusing, yet it affects all ballistic projectiles.


A lot of different and sometimes opposing forces act on a pellet in flight.

21 thoughts on “Interesting ballistics

  1. B.B.

    Missed that segment of Mythbusters. I would presume an ice bullet would melt from heat and friction long before it could do any damage.

    Springer John




  2. Markus,

    I wondered about that myself. I believe it does, but the amount of the effect is so small that it is almost imperceptable.

    I should have mentioned that precession is a fraction of the outside force that causes it, and gravity is such a relatively weak force that there isn’t much that remains when it has been factionalized.

    B.B.


  3. B.B.
    this is off the subject but was wondering if u have seen or heard of the RWS model C225 pistol and if so can u tell me the quality and value of this CO2 pistol thank you




  4. The affect of escaping gasses causing projectiles to continue to accelerate past the muzzle does exist, but you are right it is for a very short distance. It is for only 1-2 cm past the muzzle on a high-powered rifle or several cm past the muzzle of an artillery piece with a hot load. It is something you will never be able to measure with a coronagraph. I don’t know how one would measure it, but I read about it while studding internal and external ballistics.

    Ed


  5. I was wondering could an ice bullet work if fired from a PCP, or better yet CO2. A CO2 gun gets cold when fired so there would be no hot gasses, but would the rifling cause the projectile to break up. I would love to see Jamie and Adam (hosts of Mythbusters) out smarted.

    Ed


  6. Ed,

    Thanks for that fact on external ballistics.

    I agree with you that an air or CO2 smoothbore would probably work. I don’t think Jamie knew what he was doing when he made his airgun valve. I emailed to introduce him to Dennis Quackenbush and Gary Barnes, but I haven’t heard back.

    B.B.


  7. “coronagraph” guy … LOL, did u have a few cold ones from south of the border when u wrote that ? did u measure how fast the lime sank to the bottom of the bottle ?


  8. I assure you no cold ones were involved, while studying ballistics in Kingston Ontario that is north by the way. While the affects of external acceleration are negligible as far as velocity is concerned, it is the tendency to destabilize the round that concerns the artillery. This is part of the reason that crowning is so important.

    Ed


  9. about pellet drop, on my gun, a damaged grizzly, my pellets drop so dramactically i can see a black dot sinking in my scope. it actually hits the ground before making it to a target, about, say, 20 metres away. and this was done with hyper-veloity pellets, the really light ones that are said to damage spring guns. interesting. what fps, approximately, do you think i am shooting at? original fps for a pellet, as stated on the box, was 300.


  10. Ed,

    the sinking lime guy was only poking fun at the way u spelled chronograph I’m sure

    good info you gave though, thanks.

    dsw



  11. Mythbuster is a stupid show anyway. Some of their testing methods are just not scientific. Remember, they are stunt tech, not scientists. The only amusing part of the show is when they blow things up.


  12. OMG! Someone who doesn’t like mythbuster??! :-O It’s a brilliant show! Mayby not totally scientific, but i’m a true fan of them anyway :-D Btw. I have a quistion about a weird sounding HW90! I have gotten a HW90 5,5mm and i wondered if it is nomal for it to have a small “Ziiing” noice from the safety? It occures when i put’s it off safe a are about to fire. It’s really driving me crazy!! It is also there when i fires it but not so dominate due to the crack from the muzzle. I have cronographed it to 249 m/s with 14,66 grain Field target trophy, 203 m/s with 21,14gr Diabolo baracuda, and last, 277 m/s with 11,9gr RWS hobby. I posted the speeds if anyone would be interested ;-) !


  13. Here is an interesting fact concerning the ice bullet mythbusters episode. Lead, which has a melting point of 327 degrees celsius or 621 degrees fahrenheit, becomes malleable at >1000 fps, and at >2000 fps it starts to melt.

    Another reason to slow your pellets down :P, as well as another reason why ice will most definately not work in a high power rifle.

    Why didn’t the mythbusters test the MULTIPLE other ways to do this experiment? They always try to prove a myth any way they can, why not this one? Weak attempt mythbusters.


  14. Hi Rick,

    I'm looking at getting an airsoft gun that is a balance of accuracy and power, with an excellent scope and the best silencer out there.

    could you help me put together the most epic airsoft gun ever?


  15. James,

    There are no Ricks here.

    You have any idea of how much money you are willing to spend on this epic airsoft gun?

    Why do you want a silencer? Do you just like the look? They don't actually work on airsoft guns, you know.

    Are you looking for a handgun or a long gun?

    Since you want a scope, I'm guessing that you also want a long gun. Long guns don't normally use silencers, so you must have a special purpose for this. Say you owned a genuine M4 carbine (firearm). To completely silence it you'd be shooting ammo with the power of a .22 short.

    Can you please expand on what you want just a little?

    B.B.



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