too much arrow weight?

[Terry Green]

There is a point of diminishing returns with arrow weight. There is a section in one of the “Traditional Bowyers Bible”…..done remember which one. It’s a point where adding more weight doesn’t really increase momentum, it basically flat lines, while speed and thus trajectory drop like a rock.

This point was different for different styles of bow….recurve vs longbow, etc.

Yes, there is a window where the perfect weight and speed can be.

Here's a little formula if you want to run some numbers on different weights out of you bow to find the perfect combo.

Hopefully this post will clear the waters...

These 3 bows were delivered to me back in 2004 to celebrate Tradgang's 1st Anniversary. I have been hunting with the 60 & 70#ers ever since, and Rob has been hunting with the 50#er since then till about 2 years ago when he sent it to me so I could use it in my golden years. (not there yet  )

So, all made at the same time, by the same bowyer, all the same model, all the same lengths, all the same materials, all the same draw lengths.  All also use the same arrow, weight was increased for the 60#er by adding aquarium tubing and head weight change, and the 70#er with weed eater line inside the aquarium tubing and different head weight. All arrow weights were right at 9.5 grains per #, and arrow speed was right at 185-187FPS with all 3 bows. Although the speed might be relevant to the hunter, it is irrelevant in the test as long as all 3 are very close to the same, as well as arrow speed.

Here are the numbers I ran on them back then..... Kinetic Energy and Momentum.


50# - KE = 37.99 - MO = .411
                                                 
60# - KE = 45.59 - MO = .493 

Difference in Percentages - KE = 27.795 % - MO = 19%

This is a very significant increase of power in the two bows.

*************************************************************

50# - KE = 37.99 - MO = .411
                                                 
70# - KE = 53.19 - MO = .575

Difference in Percentages  - KE = 55.804 % - MO - 39.903 %

This is a HUGE increase in the power of the two bows. 

Momentum is really the most important number, and its right at a 40% Increase.

So, if the OP old_goat2 went from 45# limbs to 65# limbs, he would expect very close to those same percentages in increase of power.

 

[Terry Green]

Now even though those are 10 grain per pound arrows out of 3 different bows, you can use that formula on 9,10,11, and 12 grains per pound run though a chrono  and see where you have the best ratio for Momentum. 

 

[KentuckyWolf]

My personal library is currently in boxes….due to remodeling, but I think it was the “Traditional Bowyers Bible Vol. 1” with Jim Hamm.

So doing this from memory.

Momentum is the number we want to pay attention to. Kinetic energy is heavily influenced by speed. This is based on a difference in how you calculate KE vs MO. Compounders, riflemen and speed junkies like KE. However, in real world applications, in flesh and blood, momentum is a more reliable indicator of terminal performance. Chasing speed while slinging light arrows is why you see poor terminal performance in some “tech” bow setups. Guys shooting 70lbs at 29in draws and can’t reliably get a pass through on 100lb does…..weird right? Ha.

The relationship between arrow weight and momentum was sigmoid. As arrow weight went up, so did momentum initially. However, eventually you seen an inflection point when the gains in momentum as arrow weight goes up decreases to the point that additional arrow weight returns meniscal increases in momentum. The relationship now is almost flat.

The relationship between arrow weight was mostly linear and negative. No real surprises…lighter arrows are fast and heavier arrows are slower. At progressively higher arrow weights, past the momentum infection point, speed is lost with out a meaningful increase in momentum.

The happy medium…was to be around that momentum inflection point. Getting most of the possible momentum out of the bow (based on draw weight, design, etc). While retaining enough arrow speed to have a reasonable trajectory.

[Terry Green]

Yes, great stuff KY, can you tell my how a #70 might not pass through a #100 doe?  I know that can happen by sorry tuned bow n arrows, but not sure how with all being perfect. THX.

[KentuckyWolf]

Seen and heard about it from compounders. Shooting very light weight arrows and mechanical heads. Sometime it works and sometimes it fails.

[JamesD]

I have seen videos where sometimes the arrows bounces off out of those light weight setups as well. I know a couple of compounders that have had the issue as well.

[Terry Green]

Ah, yes. I gotcha now. The need for speed and flyback make-believe heads.

And yes James,  seen that many times in clips.

A Recipe for Disaster.

[JamesD]

Here is an example of the momentum gains on one of my current setups, and the point where the gains slow down.

43# (at my draw length of 30.5") reflex deflex long bow

10 GPP = 187 FPS (estimated from Stu Miller spine chart), 435 grains, and a momentum factor of .33
12 GPP = 163 FPS, 521 grains, and a momentum factor of .38 (15% greater than 10 GPP)
15 GPP = 148.5 FPS, 652 grains and a momentum factor of .43 (30% greater than 10 GPP)
16.7 GPP (the actual setup I am shooting) = 142.2 FPS, 725 grains, and a momentum factor of .45 (36% greater than 10GPP)

[RIVERWOLF]

Might have been better to just ask "what you like & why" ;^)

It's been proven over a lot of years that a wide range of grain weight per bow weight will "get er'done" .....

Papa Bear was in the 9-10 gpp mindset....Pretty solid background to back those thoughts 

It's hard to argue Mr. Bear's findings. 

I like many of you , have taken a few game animals (and a lot of stumps;)  with a wide range of arrow weight. I love 550gr---650 gr out of 50#-55#  Montana Longbows....it's just a deadly combo . Good speed, excellent trajectory , powerful PUNCH. This year I was using a 52# @ my 27.5ish draw and 585 gr (total) arrows with NO complaints !

I  also tend to keep the same shafts & broadhead combo , and tweak nose weight to get the tune spot on with those components . That always falls  in the above spectrum & that's good enough for me in the weight department ;^))  Changing strings , silencers , brace , etc....will determin end weight needed for perfect arrow flight ......

All with a dead quiet bow (effecient usage of the power & proper tune) , and  a VERY Tough arrow shaft. I almost always use Easton 2018's , and vary nose weight needed with  adapter weight . 


So for me....I tend to gravitate toward the heavier end of the advised spectrum for ""my needs" as a bowhunter .

9---15 gpp spectrum seems to be pretty good all around hunting weight .  Let your tuned equipment  & "your"  practice determine   what will work BEST for you and your needs........as a Bow-Hunter.