Advantage with heavy points?

[T101]

wow thanks for everyones advice. interesting information and some good verbal sparing!

shot 100yds this evening but not b4 running out of scope clearance. had to move my peep up about 1cm. hold position a little uncomfortable now though.

as i had no trouble reaching 100yds with longer arrows and only 90g points with less draw weight, those extra 20g would seem to have had a significant effect on arrow speed. however my groups are definitely tighter at all distances.

i shot a v.windy western a while back and the points really made a noticable difference. need a windy 100yd test i think to be totally
sure.

SAMBOW keep me posted on your testing, sounds scientific enough for me dude, can u still get 100yds with 125g points though?

[Marcus26]

The bending is not caused by the resistance of the weight, it's caused by string oscillation.

Originally Posted by phil_r_58

My 'A' level physics may be rusty, (1976), but isn't the bending on release caused by a moment of inertia? the point weight resisting the forward push momentarily ? And if you increase the weight, you also increase the resistance of the point to beginning to move. (Come on sp220, you're supposed to be the ace physicist, enlighten us!)

The bending on a spining jig is done by holding the arrow between two points, exerting a force in the middle, and measuring the bend. Not the same as forcing 120 grains from rest to over 300fps in microseconds.

Having said that, over the years I've heard so many claims about altering arrows that are too stiff/weak by point weight. In my experience, the effect is very small, almost at "micro tuning" level. And yes, the amount of shank in the shaft affects the stiffness.

[T101]

MARCUS appreciate your responses, u r obviously v.knowledgeable and GMB gets alot of respect in my book, i noticed that your ibo bow speed is similar to mine, and i think u mentioned shooting 120g points, with similar weight arrows, so have u had any problems reaching 100yds, can u aim on gold?

[Marcus26]

Originally Posted by T101

MARCUS appreciate your responses, u r obviously v.knowledgeable and GMB gets alot of respect in my book, i noticed that your ibo bow speed is similar to mine, and i think u mentioned shooting 120g points, with similar weight arrows, so have u had any problems reaching 100yds, can u aim on gold?

Thanks. I just listen to what many people are saying and choose the stuff that seems to match with my own findings. I have never been able to get reliable results with many of the archery accepted 'facts' that have floated around for years, and also never understood the lack of logic behind them. For example, compounders often determine arrow spine based on a left-right tear. But 20 years I watched high speed video from Easton showing compounds don't flex the arrow that way. However many still preach this.
Compound archers suffer greatly from using 'rules' that were put in place when longbow was common. These rules often carried OK for recurve, but not for compound.


Yeah Easily. With the Allegiance I struggled to make it with my high anchor but still managed with sight 6" out from the bow, but with my Constitution no problem. I have a small head so my peep gap is quite small.
When I shot 410 grain Axis FMJ's with 141grain points and inserts I still made 90m, I just moved my sight in.

[sambow]

Originally Posted by T101

SAMBOW keep me posted on your testing, sounds scientific enough for me dude, can u still get 100yds with 125g points though?

I cant get 80M with 90gn points but thats the subject of another post. I will let you know though because I need to decide by monday for a competiton I am in. So will be testing at 50M and 70M in next few days.

[sambow]

Originally Posted by phil_r_58

My 'A' level physics may be rusty, (1976), but isn't the bending on release caused by a moment of inertia? the point weight resisting the forward push momentarily ? And if you increase the weight, you also increase the resistance of the point to beginning to move. (Come on sp220, you're supposed to be the ace physicist, enlighten us!)

Phil you are absolutely right it is all about inertia. Marcos is right when he says the spine stiffness doesn't change as the point weight increases. Its stiffness doesn't but the amount it bends will change with the point weight, that is unless arrows defy the laws of physics.

A simple experiment can illustate this. Get some hollow plastic tubing (water pipe) and try slowly pushing a 1litre can of paint across a table with it, the pipe will bend a little. Try pushing the same can fast it will bend more. Then replace the 1L can with a 5L can and push it slowly it will bend more than the 1L can slowly, push it fast it will really bend. Its all because of the inertia of the weight resisting the motion. The greater the weight the greater the resistance. Want a few more archery comparisons, make the pipe longer it will bend more, make it stiffer (replace with copper tube) it will bend less. You could give up archery and just push paint cans round all day, it would be alot less frustrating

An arrow pile is exactly the same it will resist the acceleration of the arrow, the greater the acceleration the more the shaft will bend and also the greater the pile weight the more it will bend. If the point was extremely heavy the shaft would snap under sufficient acceleration (if you could fit a 4oz point you could try this, but I wouldn't recommend it).

I agree with you though, the effect of the point weight is likely to be slight (and with very stiff shafts may make virtually no difference), because in the paint can example there is the addition of friction between the can and the tabletop wheras with a point the friction with the surrounding air will be alot less. This is born out by the easton tuning programs if you keep increasing the pile weight it takes a great deal more weight before easton recommend going up in shaft stiffness to compensate.

[Jerry Tee]

If you want to you can see exactly how much difference the point weight makes by using the 2006 Easton shaft selector. Use the 'Hunting' selector, that allows you to put in different point weights, where as the 'target' one assumes an optimum point weight for the arrow and increasing the point weight won't affect the selection.

[phil_r_58]

Originally Posted by sambow

Phil you are absolutely right it is all about inertia. Marcos is right when he says the spine stiffness doesn't change as the point weight increases. Its stiffness doesn't but the amount it bends will change with the point weight, that is unless arrows defy the laws of physics.

A simple experiment can illustrate this. Get some hollow plastic tubing (water pipe) and try slowly pushing a 1litre can of paint across a table with it, the pipe will bend a little. Try pushing the same can fast it will bend more. Then replace the 1L can with a 5L can and push it slowly it will bend more than the 1L can slowly, push it fast it will really bend. Its all because of the inertia of the weight resisting the motion. The greater the weight the greater the resistance. Want a few more archery comparisons, make the pipe longer it will bend more, make it stiffer (replace with copper tube) it will bend less. You could give up archery and just push paint cans round all day, it would be alot less frustrating

An arrow pile is exactly the same it will resist the acceleration of the arrow, the greater the acceleration the more the shaft will bend and also the greater the pile weight the more it will bend. If the point was extremely heavy the shaft would snap under sufficient acceleration (if you could fit a 4oz point you could try this, but I wouldn't recommend it).

I agree with you though, the effect of the point weight is likely to be slight (and with very stiff shafts may make virtually no difference), because in the paint can example there is the addition of friction between the can and the tabletop wheras with a point the friction with the surrounding air will be alot less. This is born out by the easton tuning programs if you keep increasing the pile weight it takes a great deal more weight before easton recommend going up in shaft stiffness to compensate.

As an angler, if I cast gently, the rod hardly bends, but if I cast the same weight hard, the rod nearly bends double. The 4oz of swim feeder that I'm trying to punch 60 yards across the river wants to stay where it is.

The changing of spine by point weight perhaps worked more, many years ago, Remember, that we only had aluminium arrows, and there where 12 levels of spine, from 1416 to 2516, plus we had the 14 thou walls and the 18 thou walls either side too, so over 20 spines to choose from. So going from say 70 grains to 125 grains would affect each arrow more. I've just looked at the pro tours on the Merlin site, and there are only 9 spines, not 12 basic, plus the 10 or 12 intermediates we used to have. So putting a heavy point in an 1816, would easily make it behave like an 1814, so you can see where the root of these beliefs comes from.

And even then, 30 years ago, we were experimenting with points, and "fads" still existed. One top archer started using screw in 125 grain field piles, shot a good score, then lots of people followed, assuming that was the secret to success. When using those piles, we found the need to go up one size, My bow, happy at 1816 X7's with 80grn nibb points, needed 1916's, with 125grn screw ins, plus the weight of the adaptor to get good flight and grouping.

String oscillation is a side to side movement caused by the string sliding of the fingers. It just waggles the tail of the arrow, not causes it to physically bend and oscillate. If you analyse the slo mo stuff, you can see the two motions existing. If you look carefully from behind, sometimes the fletch seems to stand still, then flick, or sometimes does a double jink. That is the effect of the two motions, sometimes in harmony, sometimes in opposition.

[geoffretired]

Great explanation, Phil. So the string and the arrow have their own oscillation patterns, but while they are joined, they interefer with one another, yes?
I wonder of changing bracing height can change the pattern of the string vibrations enough to give a better match with the arrow in use?

[sambow]

Originally Posted by phil_r_58

String oscillation is a side to side movement caused by the string sliding of the fingers.

Finger oscillation brings in additional forces. My explanation above relates to forces acting directly along the axis of the arrow. Bear in mind we are in a compound section, although the poster has not explecitly said so, the chances are a release is being used, the arrow and string will still oscillate side to side but not due to finger rolling effects.