Stealth_Force

OK...now NORMALLY I admit, lighter arrows WILL have less KE than a heavier one shot out of the same bow.
Now THIS happens! Just when I was ready to stick with 100gn tips, or go to 125s....Just for the heck of it (buddy wanted to see "what'll she do?&quot I slapped on some 75 gn tips. Gained 13fps...and .5lb KE!!!
OK...now I have flatter trajectory, AND more KE...sounds the same (not a perceptable change).
So...with more speed and KE...no change in noise...WHY should I go heavy again??? (LESS KE! with MY set-up)

Edited by - mdbohuntr on 11/29/2002 11:43:56

tm

I've seen this many times, generally from underspined arrows. Most of the arrow charts are off on the weak side and will result in the arrow being too weak to absorg all the energy out of todays bows. 13 ft. for 25 grains is alot, should be more like 5-6 ft.
Basically what it's telling you is that the extra speed is making it calculate more KE. This however is misleading because of the loss in momentum, and the loss in downrange KE. Lighter arrows will hit with less momentum and lose more speed downrange.

jimmya

i am also interested in this topic because the only formula that i have found for KE is

arrow speed (squared) X arrow weight
divided by 450240

and buy the lookes of the formula the greatest boost in KE would be the arrow speed. if someone can shed some light on this subject it would be greatly appreciated i am planning on overhauling my bow setup after the season to get as much speed as possible. the problem is that it is going to hurt getting rid of my faithfull 2315 superslams.

AB Bow Hunter

I am no wizard @ any of this but one thing I do know is, when you are calculating the KE, you use the speed number twice, so I think by cranking her up a bit in the fps category you can get a little more bang for your buck.

Boy I bet that bang for your buck line will draw some feedback on lighter arrows being louder! <img src=icon_smile_wink.gif border=0 align=middle>

Anyway, keep in mind this is coming form someone who is over 90 lbs of KE. That mark is attainted by a 375 grain arrow traveling 330 fps, flat trajectory is important to me.

I don’t know what you are referring to as “down range” but my bow is over 90lbs of KE coming of the rest & @ 40 yards which is about all the longer I would shoot hunting, it is @ 292 fps, & 70lbs of KE.<img src=icon_smile_big.gif border=0 align=middle>

PS: The bow is still amazingly quiet, the dam arrow flight is loud! Are vanes quieter than feathers in flight?


Good judgment comes from years of bad judgment.

AB Bow Hunter

I am glad to see some brought up the fact that down range everyone losses fps & KE. My brother shoots a Legacy, 64 lbs, 28” draw & ACC 3-49’s. He is getting 255 fps & 57 lbs of KE off the rest, but @ 40 yards he is just @ 44 lbs of KE & 228 fps. You could get into a situation where shooting mech. heads may keep you from taking a longer shot.

If you ask, people are saying that you need anywhere from 40-50 lbs of KE to open a mech. head correctly. My brother will not take that longer shot unless the deer is perfectly broadside.

If you want to play with numbers, & figures, get the Archery Program, I have found it to be quite accurate with speeds, a little too much on arrow drop, (probably more my shooting). <img src=icon_smile_evil.gif border=0 align=middle> http://www.thearcheryprogram.com/


Good judgment comes from years of bad judgment.

Stealth_Force

Hey, that's the program I use!!!
Pretty much, whenever a manufacturer says to use 55 Lbs/ft of KE....that means at point blank. they realize than down range you will not be at 55 anymore.
I have also had issue with this 55Lbs minimum for mech heads (rocket suggests velocities...nothing else) does it REALLY take up THAT much energy to open a mech head? I doubt it (gonna do some tests with mech heads, and fixed heads shooting through deer hide to find out for SURE how much harder it is).
According to TAP(The archery progam) With either set up, i'm at about 51lbs/ft @30 yards, and 48lbs/ft at 40.

Trushot_archer

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

&quot;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 &quot;throws&quot; 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 &quot;slugs&quot; and is then multiplied by the speed of the arrow to determine the momentum, expressed in slug-feet per second&quot;.

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 }}------>

Stealth_Force

No offence, but that's a load of BUNK!
bullets are NOT arrows, they mushroom while arrows cut. apples to bolling balls!
To relay numbers from ACTUAL TESTS (Bowhunter Dec/Jan 1999)
Ethafoam
Arrow #1 400gn 244.88 fps KE 53.28 penetration 12 1/32&quot;
Arrow #2 600gn 200.88 fps KE 53.78 Penetration 11 15/16
Styrofoam (same arrows as ethafoam test)
Arrow #1 13 3/16&quot;
Arrow #2 13 1/16&quot;
These tests while not on actual animals, tests ONLY the differance in penetration through controled substances
NOTE: The lighter/ faster arrow had LESS KE, and MUCH less momentum...yet penetrated BETTER!!!
While a slender broadhead (Steelforce) should cut hide better than a stubby blade (Slick trick) It is the stubby head that penetrates BONE better (less surface area...works EVERY time in my tests). I don't think many worry about ANY head penetrating hide...but bone is another matter.
Of those 2 heads, both are 4 blade heads, and the slick trick has a LARGER cutting diameter! (should do even WORSE, but it does NOT)
Momentum, is NOT as good at estimating penetration as KE...and even KE has flaws..but is much closer than momentum.
HERE WE SEE ARROW #1 HAS .437 SLUG/FPS AND #2 HAS .5357 SLUG/FPS MOMENTUM.
LESS momentum penetrated as well or BETTER than MORE momentum! But the KE was nearly identical!
Again, NO offence, but I will take real data (even slightly NON scientific tests) OVER bullets vs. arrows ANY day of the week.

AB Bow Hunter

Like I said I am no wizard @ any of this, but what do you think?

I am shooting a 375 grain arrow 331 fps, with a 75 grain mech head, mini-blaster 3. My KE is over 90 lbs, my momentum is .55 slugs/fps momentum. This should certainly blow through anything in it’s path, bone, hide, any animal correct??


Good judgment comes from years of bad judgment.

Edited by - AB Bow Hunter on 11/30/2002 22:13:18

Stealth_Force

Any animal at any time? No. Animals can turn (deflect arrow) I would like to see any arrow go through the largest section of the front leg bone (Not saying it can't....but I'd like to see it)
I have seen a cut on impact head go about 20-25&quot; into a cape buffalo after being shot out of a 100 pound draw bow and stop! (yes, a compound).
You should have very good results, but I would NOT gaurentee a pass through on any animal every time.
being a rocket head, I'm sure you get your share of pass throughs...but again, NOTHING is for sure.