The Effect of Point Weight & EFOC & UFOC on Arrow Trajectory

[Paolo Mauritania]

 

[Buffalo1]

I have heard Ashby at 2 presentations and had 1 private conversation with the man. He is simply the "guru" of FOC. He can explain easily and with facts. He cuts thru the bull. FOC is real. Great video. Tks for sharing.

 

[Paolo Mauritania]

Welcome. I have gone through all Dr. Ashby documents and updates when I decided to get up to 75 lbs LB, and rather than spending more in bows to increase poundage further, I realized that I better spend money and time on better arrows. He's at au pair with Hill and Pope when it comes to contribution to bow hunting, and it makes little money out of it.

 

[KMG Hunting Safaris]

Thank you very much for sharing. Would have liked to see him add a crony to the tests and compare velocity drop over the heavier filed tips.

 

[Paolo Mauritania]

My to cents. I am more concerned with the downrange speed and momentum scenario.

Lighter arrows shot from the same bow as in the clip, have two things that cause them to decelerate faster than heavier arrows: first the mass is lower thus the drag force has a larger effect, and second, the higher velocity will cause the drag force to be larger (speed squared is at the denominator of the drag equation). There is indeed a loss of speed at departure passing from lighter to heavier arrow, however the loss of speed downrange is less for the heavier arrow, even though it start slower it shed speed at a much lower rate. The initial higher momentum of the heavier arrow, shed at a slower rate as well.

Given that in the test the same bow is used, the trajectory change from lighter to heavy (100 - 315 grains), at 35 yards, in the the worse scenario is 4" (10 cm) difference; I'll take that for higher bone breaching power and heavy hide penetration in the event of a none-perfect shot. If the chap would have done the test at 50 yards the drops would have been considerable, but with my LB, I do not shoot at yards, I think is a stretch, but this is me.

For the string jumping impala, I would not go for super heavy mass, just enough to have a good chance to breach the hide, short flight, and look for that tad of a speed more, given that their reaction time is in the range of millisecond.

https://www.omnicalculator.com/physics/impulse-and-momentum#formula-for-momentum

This is a link (not an archery calculator link) that, given both start and downrange speeds (fps), and arrow mass (grains), will calculate downrange momentum, playing with the number will clarify.

Worth mentioning that as result of Dr. Ashby "Natal study" (1981-1985), in 1986, if I remember the date correctly), SA made bow hunting legal. He must have said something right.

 

[Dee S]

I could go for lighter and faster for 3D shoots, but the best example I've seen for light and heavy arrows for hunting is the game of darts, played in bars all over the world. The old, heavy, weight forward darts we had as kids seemed like they weighed a pound. But barely toss those rascals and they'd still bury into the dart board. Then came along these fancy, skinny darts and now you had to put some 'umph' into your movement, otherwise they'd bounce off the board.
To each their own, shoot what you feel comfortable with and to heck with what everybody else says.
I admit though, I drink from the Ed Ashby kool-aide pitcher, and it tastes good.

 

[Tra3]

@Dee S i am sitting next to you with the same glass of kool-aide!

There is velocity loss with a heavier arrow, but the 650 grain setup I shoot flys better, is quieter, and has a lot more penetration. Even when I shoot longer ranges (70-100 yards) the penetration is still significant.

 

[Paolo Mauritania]

Tra3,
Couldn't agree more, a little attention, to what changes and what does not, downrange makes intuitive that arrow mass does not change, no matter how far it goes; speed shed, no doubt about that, but lighter arrows shed speed at a much higher rate than heavier arrow.
All considered, I do not shoot at the same long distances, but within the average hunting distances 15 to 35 yards, trajectory is not an issue at all, and terminal impact performance (impulse momentum), as compared to what Dr. Ashby calls "normal arrows", even from relatively heavier bows, is more than adequate for virtually any large size animal, including cape and water buffaloes (interesting are his field tests reports of the 50# bow versus the 70# and 80# range bows).
Normal arrows are defined as those not having all or part of the 11-12 penetration enhancing factors researched and field tested by Dr. Ashby; among these the so called "bone breaching threshold" mass of 650 grains.
Dr. Ashby is still probing the lower poundage bows (#40) threshold of acceptability for certain size of animals; however, the message is clear, shoot as higher poundage bow as you can effectively (and accurately) handle, once you are there, what makes the difference, sometime a big difference, is the arrow system.
There is little point working exclusively on poundage, and shooting sub-par arrows built with no considerations for what happens when the arrow get there, and needs to penetrate a heavy bones and tissues. So-so shots are the majority, over perfect shots. Speed sells, but speed alone is not what makes the kill, or the pass through that dispatch the animal fast and humanely.
My two cents.