That was the original question I think. Using a Hollow Point or Soft Point bullet would be more humane than a FMJ. I don’t think there could be any argument there. Can the .223 FMJ do the job? Of course, but it isn’t the best choice. For a bullet to be efficient, it has to give up its’ energy into the object being shot, causing massive shock. Since the FMJ doesn’t mushroom like a soft point or fragment like a hollow point very little energy is transferred, and unless a vital organ is punctured causing it to bleed out or large bone is hit casing the fragmenting with bone matter, the bullet may not kill the animal.
If I understand correctly, the Geneva Convention was to make war more “civilized” and disallows anything but a FMJ because it causes a cleaner wound that when not lethal, can be recovered from easier. (Fewer bits of clothing or foreign matter get dragged into the body as happens with hollow point or soft bullets.) The military uses them because they feed more reliably, not because they kill better. I know Vietnam Vets that loathed giving up their M-14s for the M-16. Their comments were that the .223 was ineffective against drugged up/hyped up combatants while their .308 M-14 put them down nicely. I have read some GIs liked to cut the tops off their .223 bullets making them into soft points, to increase their killing power. (I think they were called dum-dums and were a no-no.)
As far as the odd bullet path of the .223/5.56, it was my understanding from the experts while I was in the military that it was caused by the rate of twist in the Colt M-16 not stabilizing the bullet well. If this is the case, it would act differently in different rates of twist.
Yep, it was the twist rate for stabilization of the 55 gr M193. Now all spitzer type bullets will yaw and tumble given enough depth... some spitzers will do this better than others. Twist rates also influence the amount of yaw and tumble. Range also plays into the equation... closer the range, better the yaw and tumble.