At a recent Long Range Training course we had a spread of calibers – 223, 270 and 308. If you were to take a guess at which one was able to be shot out to the longest distance before the projectile slowed down and came back through the Transonic Zone (mach 1.2) it would be a bit of a toss up. 308 projectiles have a higher BC than 270 projectiles, but the 270 fires them faster. If I had to put money down on it I would say the 308, but mainly because I have an unreasonable hatred of 270.
After calibration, including velocity and atmospheric testing, we were able to establish that the 308, firing a 150 grain soft point projectile, had a supersonic range of 510 meters. The 270, also firing a 150 grain soft point projectile, had a supersonic range of 490 meters. If you think that’s strange this this is going to mess with you even more – the 223 shooting a 55 grainer was supersonic at 510 meters also and even had less wind drift than the 270 at the same range.
So why did the 270 perform relitively poorly? There were a few reasons but the bulk of the answer is simple – Ballistic Coefficient. The 270 projectile had a lower BC than the 308 projectile. I’m not trying to make the claim that there is no potential for the 270 cartridge, or any high case volume cartridge, to successfully shoot at long range. But what I am saying is that if you are purely looking at raw data on case capacity and making judgements on performance potential you’re being very ignorant.