Shorten arrow or remove a little from the point weight

Sinbad

Member
Hi All,

380 pro tour 29" with 125gr points. They are shooting alright, but to get them to act fully as they seem a little weak, i have dropped the bow down to 52lb (usually shoot it around 55lb), it also made the bow sound a lot noisier and went quiet when wound down (I don't like noise from the bow).

To give it a little more strength so i can put the poundage back up, would it be best to remove a little of the arrow or try it with a little less point weight. I could take an inch off without issue, and the points have break off parts of 10gr.

I know doing the points first would be easier, but would the weight loss still give the noise, or by making it react stiffer, so putting the force more into the arrow keep it quiet (not after speed as i don't have an issue with distance)

Cheers
 

ArcheryFox

Active member
I generally tend to find that point weight is worth relative peanuts when it comes to tuning (or at least only very fine corrections), so my suggestion - if the arrows really were behaving weak - would be to take a little length off the front.

I've run a rough setup (55lb Invicta 40, 28" DL) through Archer's Advantage for you, and 29" 380 protours with 125gn points come out as 'optimal spine' for a starting point.
Removing 10gn from the point makes negligible difference, whilst removing 1" pushes them into the 'slightly stiff' category.
On a modern compound I wouldn't be too concerned about this change as it is relatively small, it's hard to go too stiff for most at these poundages, and stiffer is the safer side to be on.

If you are concerned with noise then, if anything, you want a heavier arrow to take extract more energy from the bow rather than a lighter one!
Since you don't need speed I would consider trying more weight, though the protour is already one of the heavier shafts on the market, especially in the 380...
AA suggests your GPP (grains per pound) is about 7 which is well within the 'safe' range before noise and vibration usually becomes an issue.
It may also be worth checking for the source of the noise before you commit to anything - were the arrows contacting the rest or was the rest vibrating differently in the previous setup?

Tl;dr I'll leave it up to you as to what tests you run to decide that they are weak - it's entirely possible - but if this is the case I would probably consider taking a little off the front. I'd be tentative cutting however, as this setup sounds reasonable, and would check for the source of the noise first. As always with arrows YMMV, and I accept no liability for what you do to a set of protours!! ;)
 
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KidCurry

Well-known member
Think I would look at the noise first. I used to shoot 380s at 29" nock to end of shaft with 120gr points at 59# with no issues although they were very slightly soft from my PSE Supra Max. Check all the usual setup stuff like timing, brace height etc, you know the stuff to check. Last resort cut arrows :) What is the bow and setup?
 

Sinbad

Member
Invicta 40". Checked brace etc, both ends out the same turns and hits the wall perfect, not hitting anything, arrow rest is bob on at the right height etc. Everything is tight as should be. going to take everything off again to see if something else is the cause of vibration and noise. It does give good flight etc, so no worries on that.

If i took them down a little, even though they would be lighter in weight, would it transfer the energy better to the arrow as it would act a little stiffer?
 

ArcheryFox

Active member
No, a stiffer arrow is harder to bend with the same poundage (force) so will flex less, but stiffness does not affect energy.

Assuming the same draw force curve applies the same forces to all arrows, the energy stored in the bow is:
BE = F*DL

When released, this stored energy is turned into kinetic energy of the form:
KE = 1/2*m*v^2

But not all of the bow energy goes in to the arrow - some also goes into moving the string, limbs, cams etc.
So we can write:
KE = 1/2*(m_arr + m_bow)*v^2

Since we require (by physics) all of the stored energy to go into kinetic (plus a small amount of heat):
BE ~= KE

The percentage of the stored energy that goes into the arrow is therefore:
m_arr / (m_arr + m_bow)

So the heavier the arrow, the more of the bow's energy it will extract.
Any energy that is not extracted into the arrow is left in the moving parts of the bow to be dissipated by vibration, generating noise.

This can be a little counterintuitive to get your head around.
A lighter arrow _will_ be accelerated to a higher speed than a heavier one, but it will extract less energy from the bow.
A lighter arrow will also lose energy due to drag faster than a heavier one (though this is more to do with a balance between momentum and energy).

F = draw force on arrow, m_arr = mass of arrow, m_bow = mass of moving parts of bow, v = speed, KE = kinetic energy of arrow, BE = bow energy, DL = draw length.

-----------------

Returning to the matter at hand - I ran the arrows through AA for a 55lb Invicta 40" and all seems bang on (see above).
Now, AA is not perfect 100% of the time, but having also shot 29" 380s from a 59lb bow that behaved stiff, I would have thought they should be fine for you, and surprised if they're weak (though it is possible).
If I may ask, what led you to conclude that they are weak?
Regarding increased noise, sometimes a change of setting can make a bow sound louder. I always find my bow suddenly sounds very noisy whenever I go from outdoors to indoors where our range roof is quite low.
 

Sinbad

Member
The arrows seem to do a lot of flexing (not fish tailing) as they travel. but they do go straight, I will do some tests and may just leave them as is. paper tune etc shows them spot on.
 

ArcheryFox

Active member
Some more rigorous testing would be good to confirm.
Paper tuning is a start and will show up extreme issues.
Be aware that it can also be sensitive to technique (e.g. hard torque), contact issues, and bow-paper distance as well as the arrow stiffness.

The best way to go (IMO) once paper tuning has you in the right ball park (which I think you should be) is group tuning.
Tweak the poundage up and down and compare group sizes at distance.
John Dudley has written a lot on this - look up his HIL method I think.

Alternatively shoot different distances and look at the groups.
Stiff arrows tend to perform a bit better at close range, weaker at long distances.

To be honest, however, I have rarely tried HIL/group tuning and just getting the right ball park, not being too weak, and checking performance across a range of distances is enough to shoot at a fairly high level.
 

Sinbad

Member
Well as we cant shoot at the field for a while, i will have to do what i can at home. Strip everything off to check for noise, make sure its something i have not missed. Thinking of hand grip, i may take a look at that, as i do think that it has changed going from the PSE that i had padding on to the hoyt, may be putting a little torque in that is causing the string to no go into the groove fully.

Cheers guys, will update when i find it.
 

KidCurry

Well-known member
The arrows seem to do a lot of flexing (not fish tailing) as they travel. but they do go straight, I will do some tests and may just leave them as is. paper tune etc shows them spot on.
Have you paper tuned at different (short) distances? I only usually use paper tune for torquing usually but this is one exception where it may give you more information.
 

Sinbad

Member
Only at a single distance around 4ft from the paper. Tail was left changed the rest and all sorted. May need to go back a few more feet to see if it changes.
 

jerryRTD

Well-known member
Paper tune is not always reliable it will only tellwhat the arrow is doing at a single distance from the bow. you need to do a bareshaft tune
 
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