Light Spear (equivalent to a javelin): 2 pounds, 50 mph, 1" diameter
Heavy Spear (equivalent to a Roman pilum): 5 pounds, 25 mph, 1 1/2" diameter
Light Atlatl Dart: 3 ounces, 85 mph, 1/2" diameter
Heavy Atlatl Dart: 6 ounces, 70 mph, 5/8" diameter
Kinetic Energy Hunting Usage 
< 25 ft. lbs. Small game 
25 - 41 ft. lbs. Medium Game (deer, antelope, etc.) 
42 - 65 ft. lbs. Large Game (elk, black bear, wild boar, etc.) 
> 66 ft. lbs. Toughest Game (cape buffalo, grizzly, etc.) 
MOMENTUM CALCULATIONS:
In descending order
Projectile Weight Velocity Momentum 
Heavy Spear 5 pounds 37 fps    5.75 slug-feet/second 
Light Spear 2 pounds 73.5        4.57     
Heavy Dart 6 ounces 103          1.20     
Light Dart 3 ounces   125           .73         
SECTIONAL DENSITY CALCULATIONS:
In descending order
Projectile Weight Diameter Sectional Density 
Heavy Spear 5 pounds 1.5" 2.222 psi 
Light Spear 2 pounds 1" 2.000 
Heavy Dart 6 ounces .625" .960 
Light Dart 3 ounces .5" .750 
 How Hard Does It Hit?
www.thudscave.com/npaa/articles/howhard.htm -