O.K ....this is gonna be long! I dug this out of an old Traditional archery Magazine...

"It's best to start where we stand now. Almost everyone agrees that a heavy broadhead tipped arrow will penetrate better than a light arrow. Some very well known bow hunters point with pride to their kinetic energy generated with a fast bow.

Unfortunatley, kinetic energy doesn't mean squat when it comes to predicting how well a projectile will penetrate! I know that statement raised a lot of eyebrows, but it's true. To demonstrate, try shooting a 5 gallon bucket full of sand with a 230 grain full metal jacket.45 ACP round at 835 fps and also with a 550 grain broadhead tipped arrow at 200 fps. The bullet won't penetrate completely while the arrow will. If the KE buffs were right, the .45 with aprox. 335 ft.lbs. of ke and a 635 fps advantage should penetrate farther than the measley 49ft.lbs. generated by the arrow.

Why doesn't it? The answer is both simple and complex. KE formulas are great on paper, but in real world, several factors come into play. The friction of the medium, in above example-sand, plays a tremendous role in how well a projectile will penetrate through that medium. Likewise, the MOMENTUM of the projectileand it's shape as it passes through the medium are primary factors in determining penetration.

Kinetic energy is vitally important for understanding how high velocity projectiles, such as bullets, act when striking a living target. In these instances the high forward velocity and high rotationl speed do impart tremendous energy to living, moisture laden tissue. As the bullet impacts, it has what we call an impulse effect. It imparts some of that high forward velocity to the tissue it contacts, immedietly accelerating those tissues to the same speed as the projectile. These high speed tissues than move along the paths of least resistance, creating tremendous temporary wopund channels and dramatic shock effect to the animal. Likewise, the rotational effect literally "throws" tissue away from the bullet, just like the spin cycle on a washing machine. all this falls together into the general explanation for hydrostatic shock.

Blunt and Judo tips work the same way.

As bowhunters, we all know that our broadheads kill big game by causing hemorrhaging, not by delivering tremedous shock to the quarry.In order to do that the broadhead must penetrate the animals vital area, cutting through organs and severing arteries to cause both internal and external bleeding.THAT penetration is best determined by understanding the relationship between momentum(inetia) and resistance(friction). The reason the arrow penetrated the sand is that it's forward momentum was enough to overcome the friction caused by the sand.

The momentum of an arrow is fairly easy to compute. It's based on the arrow's weight and it's speed. Unlike the KE formula the speed is not squared. Giving equal value to weight and speed helps explain why heavy arrows penetrate better than light ones. It is expressed as Momentum = mass x velocity.

The only tricky part is determining mass.you must first take the weight in grains and divide it by 7,000 to determine the weight in lbs. After determining the weight in pounds, you must then divide that result by 32 ( for the force of gravity). The result of the equation is expressed in "slugs" and is then multiplied by the speed of the arrow to determine the momentum, expressed in slug-feet per second".

Let's take a look at the arrow we used to see how well it will penetrate.
WT.=550 grains
Vel.= 200fps
For the equation:
mass=550/7000=.079 lbs.
Then .079/32=.0025 slug
finally
.0025 x 200= .5 slug/fps momentum

Now, what happens if we drop the arrow weight to 360 and gain an extra 80 fps in speed?
Wt.=360
Vel.=280
mass=360/7000=.51 slug
Then .51/32=.0016
finally
.0016 x 280= .448 slug/fps momentum

Now all other things being equal the heavier will penetrate better.

If we try the KE formula, the 360grain is at 62.7 and the 550 is at 49!

The only factor we don't have data on in the equation is the resistance caused by the design of the broadhead. We do know some designs penetrate better than others. Broadhead width and shape are important factors in determining penetration. A broadhead that is long in relation to it's width would penetrate easier than a short stubby one (slick trick??)

Simply put, the larger the game, the more momentum necessary to penetrate the animal. The formula for momentum will give you a much better idea of how your arrow will penetrate than the one for Kinetic energy.


Thoughts, Comments???

Trushot }}------>