I emailed NAP for a buddy of mine who was curious about the kinetic energy of his setup and the NAP Scorpions. Here' s the reply from NAP.

We publish a minimum specification for all of our mechanicals of 50 FT/LBS. Depending on your set up and arrow weight you may be able to use a much lower KE than this. However that is a personal choice.

Few people realize that broadhead penetration has very little to do with broadheads. Rather, penetration has almost everything to do with arrow flight. A well tuned 50 pound bow with arrows that fly without wobble penetrates better than an 80 pound bow with aberrant arrow flight. Probably the greatest disadvantage of mechanicals in general is that as a group they tend to be much more critical of arrow spine than replaceable or fixed bladed broadheads. For instance, because there is a loss of energy of about 1 to 3 ft/lbs. when a Spitfire contacts a target, and because this energy loss is directly opposite the direction of travel, an improperly spined arrow will have an additive effect. Generally an improperly spined arrow fails to penetrate well regardless of broadhead style because the energy is partially lost in some direction other than straight forward when the arrow strikes an animal. A standard broadhead in this scenario would most likely penetrate and stick in the animal with enough of the shaft inside to lodge it until the animal does something that causes the shaft to break or possibly get pulled out during escape. Spitfires along with most other mechanicals will almost instantly back out because of the additive effect of the spine related energy loss, reverse energy of opening the blades and the fact the blades can close easily preventing any anchoring effect. Arrow flight is especially important on high angle shots. If the arrow is wobbling back and forth or up and down, then when it hits the target/animal the energy continues to the side rather than straight forward. On a mechanical this would have the effect of pivoting the broadhead and reducing penetration. Keep in mind that if your arrow flight is good then increased angle has NO effect.

Another thing to consider is momentum. Momentum is often disregarded in archery because people tend to concentrate on kinetic energy. Let me explain the difference. Kinetic energy is the impact energy of the projectile. It is a very good way to determine how efficient your bow transfers stored energy in the limbs to dynamic energy in the arrow. For the most part kinetic energy in the 50 ft/lbs. to 60 ft/lbs. range is ample for taking animals in the deer to elk range. Kinetic energy in the 60 ft/lbs. to 70 ft/lbs. will effectively take any animal in North America. For example, Chuck Adams took his 1400 pound Kodiak Grizzly Bear with about 65 ft/lbs. of kinetic energy. I believe he used an arrow in the 630 grain range that traveled about 220 fps. While there are several arrow/speed combinations that would produce 65 ft/lbs. of kinetic energy, Chuck opted for a heavier slower arrow because of the momentum. Momentum is the ability of the projectile to continue in motion. Momentum is a linear function of mass. The idea is the greater the mass the more resistance is required to slow or stop the object. Think of it this way if someone were to pitch a baseball and a bowling ball to a batter, and both balls had the identical amount of kinetic energy even though one is traveling very fast and the other is traveling very slow. The batter would be able to hit the baseball and move it in the opposite direction very easily while the bowling ball would most likely break the bat. The bowling ball has tremendously greater momentum and therefore is much more difficult to stop or slow down.

Hope this helps.


Cary J. Pickands
Technical Support Specialist
New Archery Products, Corp.
7500 Industrial Drive
Forest Park, IL 60130
800-323-1279