Effects on Ballistic

Transonic Problem


When the velocity of a rifle bullet fired at supersonic muzzle velocity approaches the speed of sound it enters the transonic region. In the transonic region, an important thing that happens to most bullets, is that the centre of pressure (CP) shifts forward as the bullet decelerates. That CP shift affects the (dynamic) stability of the bullet. If the bullet is not well stabilized(a perfect spiral football throw), it can not remain pointing forward through the transonic region (the bullets starts to exhibit an unwanted coneing motion(wobbly football throw) that, if not dampened out, can eventually end in uncontrollable tumbling along the length axis). However, even if the bullet has sufficient stability (static and dynamic) to be able to fly through the transonic region and remain pointing forward, it is still affected. The erratic and sudden CP shift and (temporary) decrease of dynamic stability can cause significant dispersion (and hence significant accuracy decay), even if the bullet’s flight becomes well behaved again when it enters the subsonic region. This makes accurately predicting the ballistic behaviour of bullets in the transonic region very hard. Because of this, marksmen normally restrict themselves to engaging targets within the supersonic range of the bullet used.

Discussion

  • justin4jesus

    Very interesting information! The last sentence you stated “marksmen normally restrict themselves to engaging targets within the supersonic range of the bullet ”

    Do you mean they restrict themselves to the sonic range of the bullet? If not please explain further.

    Thanks

  • http://longrangeshooter.com Sean

    The term supersonic is used to define a speed that is over the speed of sound. At a typical temperature like 70 degrees Fahrenheit, the threshold value required for an object to be traveling at a supersonic speed is approximately 1,129 ft/s, 770 mph or 1,238 km/h. Speeds where only some parts of the air around an object (such as the ends of rotor blades) reach supersonic speeds are labeled transonic (typically somewhere between 900 ft/s and 1,300 ft/s).

  • justin4jesus

    So how would a target be in a supersonic range? I’m not comprehending the last sentence of the original post. Keep in mind I’m a novice.
    Thanks

  • http://longrangeshooter.com Sean

    Well as an example, the minute my bullet leaves the rifle it is traveling at 3,200 ft/s. As it goes down range it starts to slow down and at 5,500 feet altitude. My bullet doesn’t cross the speed of sound (1,129 ft/s) until about 2,000 yards. So I should be able to shoot out to 2,000 yards without ever passing through the transonic region. But at an altitude of about 500 feet, I pass through the transonic region at about 1,200 yards. Now, if I were to shoot farther than 1,200 yards my bullet would start to become unstable. So try to keep your shooting above the speed of sound for whatever altitude you are at, otherwise you will start to lose your accuracy.

  • Frank Matchung

    This post was plagiarized, its a direct copy and paste from Wikipedia: https://en.wikipedia.org/wiki/External_ballistics#The_transonic_problem Please cite your sources of information especially when you do a direct copy an paste.

  • Charles TheHammer Martel

    There’s a free app for smart phones, called Strelok. It shows just how many variables are used to determine things like how far a particular bullet will stay supersonic. However you do the math, once you’ve done the ballistic calculations, youll know approximately how far your round used, will remain supersonic. Then you just make sure you’re at least that close to your target, and no worries.

    So if you’re shooting a bullet you know the average muzzle velocity is 2800/feet per second, you can use the bullet’s weight (like 5.56 mk262 bullet weighs 77 grains), and it’s ballistic coefficient, to determine how far that bullet can go, while still supersonic.

    If you’re a sniper, trying to take a long shot, you’ll also need to know the area’s Height above sea level, and the weather (barometric pressure, humidity, temperature, and of course, wind speed & direction)..

    Keep in mind, like you, I’m an unexperienced novice. I just pick things up quickly, and I learned how submarines used to target and hit ships successfully, without electronics, using the ship’s size (height of the ship above the water surface, and the length), and how many dots it took up on their Periscope reticle. It’s a proven system used even today, by snipers scopes, called the mil-dot scope, using Millirads. The other scope reticle is the MOA, minute of angle, I believe. Or Minute of Accuracy? I’m not sure.

    To give you an example of how different each factor can effect a bullet’s supersonic range, and bullet drop- The expensive Trijicon fixed magnification scopes, ACOGS, for 5.56 alone, have many different models, to accommodate the most popular bullet weights used by military & police: 55grain, 62 grain, and 77 Grain. If the reticle is listed in the Strelok app, you can use that app to figure how to use that reticle for other bullets as well as the one its designed for. Which is good, considering their ACOG scopes average $1200-$1500. It would suck if you had to buy multiple Scopes for the same rifle, and change them out anytime you switched from shooting 55grain, to 62 or 77 grains.