Don, there was a time in the early development of the 5.56mm when the rifling twist rate was found to 'understabilize' the bullet, and supposedly, the round was reported to cause horrible wound channels from early battlefield reports. When the 5.56mm was "improved" for greater accuracy, and the twist rates changed to properly stabilize the bullet, the "lethality" was diminished. If you get the time, look up the "Ichord Hearing Report" as reported in the Atlanta Monthly Journal. It really is a fantastic read. The report is an easy read, and covers exactly what you mention, as well as the Army Ordinance Department's role in making major changes to the early (and disastrous) propellants and M16 rifle design.