why such heavy arrows?

[wingnut]

The KE would have been about 3% more then the arrow we were using but the Momentum would have been .671 and shot through 2 elk.

Mike

[country roads]

would like to really think everyone for thier time i think i got it, i need to drive a dump truck to the woods unload my volkswagon drive it to my stand shoot a 4 pound arrow with a 1 pound head at a deer and if i hit it i use a dart to kill it with,  and they said this trad stuff would be hard

[lpcjon2]

Think about what is the most common grain weight trad head in the past 30+ years.125gr so add it to a wood shaft and sharpen it up and hit your mark. Then gut your kill and eat it. Keep it simple, then dabble in the tech stuff.Simple has been around a lot longer than the tech stuff.JMHO  

[CG]

I'm not into measuring KE. But, it seems that many think that KE goes up with lighter arrows and speed-wrong. Take any bow, and the heavier arrow will still give more KE.

[Javi]

Originally posted by CG:
I'm not into measuring KE. But, it seems that many think that KE goes up with lighter arrows and speed-wrong. Take any bow, and the heavier arrow will still give more KE.

Since the formula for Ke is KE= 1/2 MV^2 m= mass, v= velocity

Mass X Velocity squared.. Velocity is still the driving force... as mass increases and velocity drops the Ke does not increase as it would with a drop in mass resulting in an increase in velocity..

[Stumpkiller]

Originally posted by lpcjon2:
Think about what is the most common grain weight trad head in the past 30+ years.125gr so add it to a wood shaft and sharpen it up and hit your mark. Then gut your kill and eat it. Keep it simple, then dabble in the tech stuff.Simple has been around a lot longer than the tech stuff.JMHO      

That's what I ment to say.      

I've been mired to wood, mostly cedar, for the 40 plus years I've been lobbing arrows.  Two years in there I played with aluminum and a 30% letoff wheeliebow, but they were big 'ol 32" arrows and not much lighter than cedar.  In that time the heaviest head I've used was a 145 gr Bear Razorhead.  Usually it's a 125 or 130 gr head.  I never got into African game or carbons, so I never wandered through the tables and charts of the current alchemists that turn extreme head weight into gold.  I actually consider traditional bowhunting an escape from such things.

Sorry if I/we have muddied up CountryRoad's original question.

 

Help me understand why it is advised to shoot a heavy 600+ grain total arrow out of my 53# longbow the compound shooter in me says speed kills and velocity is the begining of kenetic energy so will it hurt my bow to shoot a 450 grain arrow including 125 grain broadhead and get flatter tradjectory as long as it is shooting straight and tuning right? new at this trad stuff but love shooting it is the most addictive thing i have done dont recall wanting to shoot my top of the food chain bow this much.  

Sharp kills.  Speed isn't everthing as a fast, light arrow may expend it's energy before much damage is done.  Speed does allow a better trajectory but out to 25 yards isn't much of a handicap.  A traditional bow likes an arrow that weighs 9 to 11 grains for every pound of draw weight.  Too light and the shock is absorbed by the limbs instead of the arrow and may eventually damage something.  Most of these statements are arguable (as you may have noticed).  

I hunt whitetail deer.  My arrows weigh 580 grains, are launched from bows of 55 to 60# draw weight, carry a sharp dual-edged 125 gr head and will split ribs on both sides of a 200 lb deer and still carry through - occassionally completely past the deer and beyond - but have always produced two holes and very compromised lungs or fatal hemmoraging.  My bowhunting mentor used similar equipment to harvest deer very consistantly and had been a "traditional" bowhunter for deer all his life (never used a rifle, slug gun or compound bow or any non-wood arrow - it was bowhunting to him, not traditional bowhunting) and I followed his methods.  The only deer I hit well and lost was with a very wide Zephyr Sasquatch that was an almost straight-down shot from a treestand and, I now know, a poor angle.  

That's my story and hope it helps.

[GREASEMAN]

I beleive the 10 grn/lb of Bow weight is more than adequate,but,nothin wrong with 11 or 12 if you get good flight from them,especially if the weight is up front like say 18-21% FOC.

Just my opinion

[ChuckC]

What Javi said. . .  if calculating KE, speed is everything.  That's why it is so special to compound mfr's.  That's why I asked that earlier question of Mike (Wingnut).  

The compound allows many wonderful things and these things were accentuated by the uprising of carbon arrows.  Extremely light, extremely stiff shafts that can tolerate that torque and still fly well. The lighter the arrow, in any bow, the faster the flight.  

But all in all, if you shoot a 600 grain arrow out of any compound, I sincerely doubt you will be attaining 350 fps.  On the contrary. That would severely drop the KE for that particular combination.  

Momentum measures something different and mass and velocity are on equal footing.  A rise in either will bring up the numbers.

As brought up earlier though, there are several other factors that have a lot, maybe even more to do with penetration. .  broadhead sharpness and tip shape / size. . the straightness of the arrow as it hits the target, and even the arrows ability to maintain that straighness after hitting the target.  The target moving could affect these and negate otherwise perfect flight.

So many things. . and I am not smart enough to figure all that out.  Just get a set up that shoots well for you, stay within about 8 or 9 to 12 grains per pound of bow and go get em.

Practice til you hit well at your range, learn to sharpen those heads well, learn where you should be aiming at the critter you are hunting,and you will have done your part.
ChuckC

[raghorns]

Great thread / good info. all the way around.

When I shoot with others using light arrows and not much FOC...it is amazing how much deeper penetration I get.

I want my whitetail setup the same as my elk setup so I'm ready to go either way.

[CG]

Originally posted by Javi:
Mass X Velocity squared.. Velocity is still the driving force...  as mass increases and velocity drops the Ke does not increase as it would with a drop in mass resulting in an increase in velocity..

With all due respect Javi, that is completely false.  Look at this test that Norb Mullaney did on the Tomohawk longbow    Tomohawk Bow Test .  Using arrows from 360 to 654 grains, he reported the speed and then calculated the KE.  The 654 grain arrow had the most KE.  

Compounds are the same way. Here is another review by Norb on a Mattews    Matthews Bow Test .  Taking those results and calculating the KE (i.e. V X V X M /450240), the lightest arrow (350 grain) had a KE of 73.266, and the heaviest (650) had  a KE of 76.171.

 

Originally posted by ChuckC:
What Javi said. . .  if calculating KE, speed is everything.  That's why it is so special to compound mfr's.  That's why I asked that earlier question of Mike (Wingnut).  

But all in all, if you shoot a 600 grain arrow out of any compound, I sincerely doubt you will be attaining 350 fps.  On the contrary. That would severely drop the KE for that particular combination.  

Chuck, see the link above on the Matthews bow test.  And, Wingnut's responded to your question by saying that the KE would have been about 3% more with the heavier arrows.

As I stated before, I don't really care about KE.  I don't think it represents a good measure of deciding the killing ability of a bow setup.  I agree that it favors compounds in that,  if arrow weight is the same, it favors the faster bow .  On the other hand, even though I don't care for the measurement, I still want to point out the facts.

Respectfully,

Cooper

[awbowman]

At the risk of sounding like a techno geek  .... and if I remember my physics right guys (it has been a very long time since I have been it class), I have a different take on this.  

Kinetic Energy comes from what is known as potential energy (energy stored at rest). You cannot change these laws of physics.   The K.E. comes from the bow.  The bow basically changes "potential" energy stored in the limbs at full draw into kenetic energy at the release of the bow.  All bows will have certain characteristics (all different I might add) that makes it more or less effective at transforming its potential energy into kenetic energy.  In other words there is only so much there to capture.  I would venture to say that if you did the K.E. calcs through a range of head weights, speed will go down proportionately so that K.E. remains basically the same for THAT BOW.  The effeciency at transferring the potential energy MAY change a little in the bow as you "load" it, but it will not be much within an acceptable range.

MOMENTUM is a different story.  THAT IS WHY HEAVIER IS BETTER for penetration, but ONLY to a point.  The best is a balance between FOC and trajectory (speed).  It is a rule of thumb, but 10 gpp and 15-20% or so FOC has been "accepted" for a long time by people who don't even care WHY it works, they just know it works and we all would be wise to take their advice.  JMHO though.

[Don Stokes]

Razor sharp broadheads on perfectly flying arrows kill game effectively. Everything else is window dressing. Heavier arrows (within a reasonable range) are better for hunting because the bow is quieter and they are not affected by other influences as much as lightweight arrows. Energy smenergy, these are the important things.

[Javi]

Cooper, you didn't highlight the complete sentence….
as mass increases and velocity drops the Ke does not increase as it would with a drop in mass resulting in an increase in velocity..
The ratio of increase/decrease in Ke is driven by velocity times velocity multiplied by mass therefore the increase or decrease in velocity must always win when compared to an increase or decrease in mass…  And yes a heavier arrow will have more Ke than a lighter arrow unless the decrease in velocity is substantial.
Let’s look at a archery scenario now…

200 x 200 = 40000 x 452 = 18080000 / 450240 = 40.16
200 x 200 = 40000 x 430 = 17200000 / 450240 = 38.20
210 x 210 = 44100 x 430 = 18963000 / 450240 = 42.12
You notice that a 5% increase in velocity results in an increase in Ke of 10.2% while a 5% increase in mass at the same velocity only resulted in a 9.5% increase in Ke

Ke is not however a good judge of penetration potential it is a measure of total energy not forward motion energy. If you have a 4 pound hammer according to Ke if that hammer is swung with enough force to reach 100 fps speed it would have a Ke of 100fps x 100fps = 10,000 x 28000 = 280,000,000 / 450,240 = 621.89 Ke and that’s a lot of energy… but would you choose a 4 lb hammer that had a 1 lb head or a 4lb hammer with a 3lb head if you had to drive a nail..  Remember both have the same Ke…  :D
Recurve and longbows do not suffer nearly as much velocity change for arrow weight as do compounds a compound speed varies approximately 1 fps for every 3 grains in arrow weight… what do you suppose that ratio is for traditional equipment..??? I haven’t tested it because I haven’t worried about it… I shoot heavy arrows with good weight forward ratios because I hunt a variety of animals ranging from rabbits to exotics like the Red Stag and hogs here in Texas and I’m not going to change equipment every time I head to the woods.. My arrows hit where I’m looking at any range I choose to limit myself to so I only worry about driving a sharp BH completely through the animal I’ve chosen to shoot today…

[Shawn Leonard]

Josh, never hunted moose or elk, but I have seen both rib cages and bone structure and sorry but elk are not even close to a big bull moose. I actually watched a video of a guy shooting a .5 cal. round ball at about 18fps. and it bounce off a moose rib. I know of a lot more elk killed with 45-50# bows and 8-9gpp. than moose. Shawn

[Shawn Leonard]

I would like to comment on Stumkillers post above, my 8 to 9 gpp. arrows do the same thing, so what dose it matter. I actually not only get two hole but lots of pass thrus as long as I stay off the shoulder and even when I hit shoulder I get enough penetration to get both lungs as well. I beleive the well tuned bow that you shoot accurately with a very sharp head is lot more important than the weight of arrow you shoot, again unless you are hunting the really big critters. Shawn

[Javi]

Ok... went and tested my longbow with different arrow weights to see what the ratio of velocity loss is to mass..

Averaged 10 shots at each weight.. rounded numbers are...

479 grain arrow 150fps

530 grain arrow 146 fps

difference in weight 51 grains

difference in speed 4 fps

not a conclusive study by any means but it appears that the ratio at least for MY longbow is 51/4 = 1 fps per 12.75 grains.. Hummmmm I wonder... may need to pull a 600 grain and test that...

[awbowman]

Javi:

If I did this right, KE calcs are as follows:

for 479 gr = 23.94 ft-lbs
for 530 gr = 25.09 ft-lbs

1.15 ft-lb more for heavier arrow.  Pretty close (less than 5%).  Go shoot a 600 grain and a 450 grain arrow.

I THINK??? all will be pretty close which proves my point that the bow can only store/deliver s certain amount of K.E. (within reason), so slightly heavy, 10gpp works.

[CG]

Mike I somehow think we probably agree on these things--maybe just the way we are saying it makes it appear that we don't.

My only point was that people often wrongly claim that a given bow will have the highest KE with the lowest weight arrow and highest speed.  Actual data refutes that.  Even though the velocity is squared, it is still multiplied by the weigth which is typically a lot larger number (thus the reason it trumps the square in velocity).  Actual bow test data proves that (see links in my last post for proof).

Bottom line--the reason KE doesn't matter to me is not becuase it favors light arrows (because it doesn't), but becuase an arrow doesn't kill with ft lbs like a rifle.

[Javi]

Originally posted by awbowman:
Javi:

If I did this right, KE calcs are as follows:

for 479 gr = 23.94 ft-lbs
for 530 gr = 25.09 ft-lbs

1.15 ft-lb more for heavier arrow.  Pretty close (less than 5%).  Go shoot a 600 grain and a 450 grain arrow.

I THINK??? all will be pretty close which proves my point that the bow can only store/deliver s certain amount of K.E. (within reason), so slightly heavy, 10gpp works.

I’m more interested in the reason to shoot a lighter arrow and what gain if any there is from doing so..

I shoot 47lbs at my draw length (28”) so my 479 grain arrow is just barely over 10 grains per pound if I use the ratio that I saw in my testing and went to an 8gpp arrow 376 grains… what would I gain?
 
Let’s see… 479 – 376 = 103 grains… 103/12.75 = 8 fps  so my gain would be 8/150 = 5%
 
158 x 158 = 24,964 x 376 = 9,386,464/450,240 =20.85 Ke

150 x 150 = 22,500 x 479 = 10,777,500/450,240 = 23.94 Ke

So I’d give up 8.7% of my Ke for an 8 fps 5% gain in speed… and a nosier bow which I’d have to make quieter  by adding dampening weight on the string…  losing the speed I gained…  hummmmm  :D

I will shoot a 600 grain just to see if the same ratio applies.. but I reckon the 10 grain per pound is a good place to be at least for me... But shooting the 600 might change my mind and I'll bump the weight up..

[Javi]

Ok… went and tested 2 more arrow weights…

601 = 140 fps    26.16 Ke
346 = 170 fps    22.2  Ke

So that shows a ratio of grains to speed of 8.5 over a greater spread..


Guess I’m finding out that even though I simplified my life by returning to TRAD and removing all the gadgetry from my bow, I can’t turn off my engineer brain… I still got to know how it works..