Monday, April 28, 2003

Knockdown Power

The Taylor Knockout factor (TKO) is a metric that big bore proponents prefer to the more common kinetic energy number found in ballistic tables.

Where KE uses the square of velocity, TKO is the simple product of bullet mass, velocity and bullet diameter. However, there is an anomaly which makes TKO suspect as a measure of big game cartridges.

The 6.5x55 Swede with a 160 grain bullet at 2400 fps has the same TKO as a 158 grain 35 caliber bullet moving at 1800 fps. But the Swede is a legendary big game round. It is commonly used in Scandinavia to hunt moose and had a good record in colonial Africa on large plains antelope. No one would recommend a 357 Magnum carbine for moose or zebra. Yet the TKO equates the two rounds.

The Swede's performance is due to its use of heavy for caliber bullets (i.e. high sectional density) which deliver superior penetration. (Similar performance shows up in the 7mm Mauser with 175 grain bullets and the 30-06 with 220 grainers.)

TKO treats high SD, small caliber rounds as an equal to low SD, large caliber rounds. Yet, we know that SD matters.