Home Forums Hunting & Shooting Long Range Hunting Determining a load's maximum range

The transonic problem: When the velocity of a rifle bullet fired at supersonic muzzle velocity approaches the speed of sound it enters the transonic region (about Mach 1.2�0.8). In the transonic region, the centre of pressure (CP) of most bullets shifts forward as the bullet decelerates. That CP shift affects the (dynamic) stability of the bullet. If the bullet is not well stabilized, it cannot remain pointing forward through the transonic region (the bullets starts to exhibit an unwanted precession or coning motion that, if not damped 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 stays 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 behavior of bullets in the transonic region very difficult. Further the ambient air density has a significant effect on dynamic stability during transonic transition. Though the ambient air density is a variable environmental factor, adverse transonic transition effects can be negated better by bullets traveling through less dense air, than when traveling through denser air. Because of this marksmen normally restrict themselves to engaging targets within the supersonic range of the bullet used.

Doppler radar measurement method: Some of the Lapua-provided drag coefficient data shows drastic increases in the measured drag around or below the Mach 1 flight velocity region. This behavior was observed for most of the measured small caliber bullets, and not so much for the larger caliber bullets. This implies some (mostly smaller caliber) rifle bullets exhibited coning and/or tumbling in the transonic/subsonic flight velocity regime. The information regarding unfavorable transonic/subsonic flight behavior for some of the tested projectiles is important. This is a limiting factor for extended range shooting use, because the effects of coning and tumbling are not easily predictable and potentially catastrophic for the best ballistic prediction models and software.

A lot depends on the application too.

The criteria for competetive target ammo is a lot different from other uses. Snipers in current wars are making a lot of kills well past Mach 1.2.

Hunting ammo is another game altogether. Most high velocity stuff probably wants 1600-1800 fps minimum. But muzzle loaders, 45-70s, handguns, and similar can work well into subsonic velocities.

Lots of variables depending on your equipment, and purpose.