Simply the best explanation of bowhunting dynamics I've seen

[Beendare]

This is the best explanation of the factors involved in archery dynamics I've seen- Posted by Ugly Joe on another forum.
Link is to "Kinetic energy, mass, velocity,momentum online calculators-lets get it right" on Archery talk
LINK

Folks have been tossing around KE and Momentum for years....IMO.....this nails the dynamics of whats going on.

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[Mighty Mouse]

TLDR version: Your bow determines the amount of energy you have to work with (function of draw weight, draw length, brace height, and cam design). For practical purposes, that amount of energy is a fixed quantity independent of arrow choice (energy transfer to the arrow does increase slightly with increasing arrow weight, but the gain is minor). Arrow weight is the chief parameter within your control and determines how you utilize the bow's energy: lower weight = flatter trajectory, higher weight = better penetration.

Add in a couple of snide potshots directed at Ed Ashby (odd since the author comes to the same conclusion as Ashby vis-a-vis arrow weight and penetration potential) and you get the gist of the post.

 

[Scrappy]

All that mumbo jumbo and it still come down to if you hit the critter in the right spot with sufficient penetration equals short blood trail, ok got it.

 

[McD18]

That and don't use a mechanical BH... (what he said, I'm not picking a fight here).

Also he never talks about the effect of FOC.

I prefer Ranch Fairy's real world experiments.

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[5MilesBack]

Nock arrow..........draw bow.........aim........release arrow........go recover animal. Is it really more complicated than that?

 

[Btaylor]

Nock arrow..........draw bow.........aim........release arrow........go recover animal. Is it really more complicated than that?

Acknowledgin the rhetorical aspect of the question but answering at face value. I think it depends. Experience and knowledge change perspectives over time. Not everyone has an experienced mentor to teach the difference between sh!t and shinola.

Back to the question, for me personally it depends on which bow I am shooting. With my compound, it s just the weay you typed it. With the stick, I flip flop the aim and draw, so yes it is more complicated than that.

 

[Beendare]

Nock arrow..........draw bow.........aim........release arrow........go recover animal. Is it really more complicated than that?

Seems to me we take blowing through animals with the setups we are using for granted when almost every video you see shows an animal running off with an arrow dangling out.

I've seen so much crap application of these KE and MO formulas over the years on the forums...and wild swings from very light arrows in an overdraw to now the cult like Ashby crowd shooting uber heavy arrows.

Ugly Joes explanation of the physics involved exactly follows my real world experience- a vindication of sorts. Its nice to know the correct application of the math jibs with what I've seen.

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[elkstabber]

Seems to me we take blowing through animals with the setups we are using for granted when almost every video you see shows an animal running off with an arrow dangling out.

I've seen so much crap application of these KE and MO formulas over the years on the forums...and wild swings from very light arrows in an overdraw to now the cult like Ashby crowd shooting uber heavy arrows.

Ugly Joes explanation of the physics involved exactly follows my real world experience- a vindication of sorts. Its nice to know the correct application of the math jibs with what I've seen.

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Beendare, my experience has been very similar to yours, as we've exchanged conversation numerous times over the years. But man, I read Ugly Joe's dissertation a lot different than you did.

Misconception #1: he starts off with "momentum does not determine penetration". Then he states that it does kind of follow along with penetration.

Misconception #2: agreed.

Misconception #3: agreed.

In the center of the 2nd page he says that penetration is the best predictor of arrow lethality. This is wrong and I'm surprised that he made such a glaring mistake. The arrow/broadhead should be matched to the animal so that the blades do the most amount of damage and (preferably) so that the arrow just barely falls out the animal's far side. Of course, we should probably add a safety factor in the penetration, just in case the arrow encounters a heavier bone. But his point about penetration is incorrect because if we wanted maximum penetration then we'd just shoot field points through animals. That wouldn't work well (nor be legal), would it?

Then he goes and says that inertia is the key to penetration. Inertia, however, is a concept and doesn't have a formula. So then he goes and derives another formula for momentum. I'm shaking my head. He's not making sense.

Did you read it differently than this?

 

[5MilesBack]

Seems to me we take blowing through animals with the setups we are using for granted when almost every video you see shows an animal running off with an arrow dangling out.

You don't need a passthrough to kill an elk quickly. Deflate both lungs and they're done quickly.....even without a passthrough. My bull is 2016 I didn't even get a passthrough shooting 75lbs at 32 1/2" draw with a 532gr arrow going 289fps at 30 yards.........but that bull was down and dead in under 2.5 seconds. And the only thing hard that the arrow hit was the offside elbow...........where it stopped. Over the top mechanical with a small entry and FP sized exit (the blades never made it past the offside hide). But that head tore him up.

I if anyone knows that when you don't get a double lung........it can get dicey. I've taken a lot of quartering away shots, some work very well.......others not so well. Sure the animals have died either way, but tracking can be a royal pain. The quickest way to sure death is double lung. Do that, and problems are solved........with or without a pass through.

 

[Scrappy]

Nock arrow..........draw bow.........aim........release arrow........go recover animal. Is it really more complicated than that?

On archery talk it is.

 

[Topo_trekker]

That was a really good write up and video. Thanks for sharing.


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[UglyJow]

Beendare, my experience has been very similar to yours, as we've exchanged conversation numerous times over the years. But man, I read Ugly Joe's dissertation a lot different than you did.

Misconception #1: he starts off with "momentum does not determine penetration". Then he states that it does kind of follow along with penetration.

It does, at least when using a sufficient bow. However, if you purchase one of the "infinitely adjustable" bows, drop the draw down to its lowest setting and drop the draw weight to 10 lbs or so, you can use an EXTREMELY heavy arrow to get your momentum back up to the same value as many have with a hunting setup—but penetration would be terrible, because the arrow would have very little energy. However, for a hunting capable bow putting out hunting ready energy, the momentum will correlate with penetration.

Misconception #2: agreed.

Misconception #3: agreed.

In the center of the 2nd page he says that penetration is the best predictor of arrow lethality. This is wrong and I'm surprised that he made such a glaring mistake. The arrow/broadhead should be matched to the animal so that the blades do the most amount of damage and (preferably) so that the arrow just barely falls out the animal's far side. Of course, we should probably add a safety factor in the penetration, just in case the arrow encounters a heavier bone. But his point about penetration is incorrect because if we wanted maximum penetration then we'd just shoot field points through animals. That wouldn't work well (nor be legal), would it?

Ok, I'll agree here. Subtext of my post was that we are using a legal broad head. The point was it is much better to have a 1.5" blade go through the entire animal than a 2.5" blade barely get into one lung. Can we agree on this?

Then he goes and says that inertia is the key to penetration. Inertia, however, is a concept and doesn't have a formula. So then he goes and derives another formula for momentum. I'm shaking my head. He's not making sense.

Did you read it differently than this?

Inertia is measured by mass. Pure and simple. No formulas needed. The second formula I derived was an alternative expression for KE. Everyone knows the 1/2 m v^2 formula; most are unaware that KE = 1/(2m) x p^2. Most don't realize that the exact same dependence of energy on velocity (velocity squared) is observed for momentum (momentum squared). People tend to equate "KE is speed" and think that momentum is different. The relationship between energy and velocity and energy and momentum are exactly the same.

 

[Beendare]

Inertia is measured by mass. Pure and simple. No formulas needed.

Yep....thats the way I read it...no math involved. KE tells you potential raw energy in the bow....the arrow and BH determine how that potential energy is utilized.

We all know- or should by now that its best to style your arrow to the game you are hunting. It doesn't take a water buff arrow to kill a deer. Thus...just about anything in a modern compound works for thin skinned whitetails. Its when you start getting into the bigger species...or you are using a mech head that the heavier arrows shine.

Thats what I've always believed^...maybe I read into Ugly Joes commentary something that wasn't there....but it seemed to me he was on the right track.

The problems I had with penetration in my youth with overdraws and light arrows disappeared when I started bumping up my arrows weight.



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[elkstabber]

However, for a hunting capable bow putting out hunting ready energy, the momentum will correlate with penetration.

UglyJoe, thanks for showing up here on Rokslide. I couldn’t remember my AT pwd because I haven’t been there in a while.

Your quote pasted above is my primary takeaway from your dissertation. For the vast majority of us that are hunting deer/elk/moose/bear with reasonable draw and arrow weights I completely agree with you:

Arrow momentum = Arrow penetration

Thank you for your explanation. I would have followed along better if inertia had been left out of your discussion.

The point was it is much better to have a 1.5" blade go through the entire animal than a 2.5" blade barely get into one lung. Can we agree on this?

I’ll agree with your example above, but I don’t agree that full penetration is necessary. 5MilesBack and many others have made it clear that taking both lungs is most important.

In fact the most comprehensive broadhead study was/is conducted at Indianhead Naval facility in MD. It concluded that mechanical broadheads were more lethal on whitetails.

Nevertheless, the fact is that mechanical heads benefit from more momentum as well.

 

[elkstabber]

Here is a link to the study:

https://www.qdma.com/does-broadhead-choice-really-matter/

 

[KyleR1985]

One of our biggest mistakes is confusing correlation with causation. Our brains are designed to recognize patterns, and use those patterns to increase our odds of survival. We really want to survive, so our consciousness often glazes over important details that might call into question the assumptions we make based off of patterns observed. If you ask me, this is the whole point of science - to push back against what feels good or right, with as little bias as possible, and identify as much truth as possible.

I think Joe's write up is spot on.

I also think he is making assumptions when stating penetration is key - something along the lines of "assuming you're shooting a razor sharp broadhead that won't fall apart on impact, the fastest way to a dead critter is an arrow that will penetrate both lungs, even with less than optimal shot placement or angle" I could be wrong here though, and wouldn't mind hearing him elaborate a little on that point.

 

[UglyJow]

Nevertheless, the fact is that mechanical heads benefit from more momentum as well.

This is one of the most prudent points that we could make regarding mechanicals. A said irony is that somehow we have equated "light and fast" with "mechanical". Maybe it's pro-shop mentality, I don't know—but this is literally the worst way to go. Take the most inefficient head and pair it with the most inefficient arrow.

If I were to shoot a mechanical—*shudder*—I would DEFINITELY pair it with a heavy arrow. There are so many benefits.

—The arrow is going to move slower; impact forces are proportional to velocity, so the mech will experience less impact force on entry. Since mechs are by design less structurally sound than a fixed, why would we shoot them at high velocities where they will experience greater impact forces and higher failure rates?

—Heavier arrows retain a greater percentage of their energy downrange; if the animal is at 60 yards, a heavier arrow will hit that animal carrying more energy than a lighter arrow from the same bow. Mechs eat energy to open, so having as much energy there as possible when the mech needs it is paramount

—Heavier arrows have higher penetration potential; mechs generally have a wider cutting blade, so they must do more work to penetrate deep into an animal, and having the extra inertia (mass) of the heaver arrow makes this job a lot easier for the mech.

—Theoretically, the slower moving head requires less work to open than the faster moving head. In thermodynamics we would say that the slower moving head opening has a larger degree of reversibility to its opening than the faster moving head. In practice this difference in work may be inconsequential, but, at least theoretically, it's "easier" to open the slower moving head than the faster moving head.

If archers are going to use mechs, for the love of Pete, screw them on to heavier arrows.

Light and fast arrows paired with inefficient mechs are built for lack of penetration and high wound-loss rates.

 

[UglyJow]

I also think he is making assumptions when stating penetration is key - something along the lines of "assuming you're shooting a razor sharp broadhead that won't fall apart on impact, the fastest way to a dead critter is an arrow that will penetrate both lungs, even with less than optimal shot placement or angle" I could be wrong here though, and wouldn't mind hearing him elaborate a little on that point.

That's about right. We could call it assuming, we could call it taking for granted, we could call it common sense, whatever. I also consider it common sense that if you are going bow hunting you can manage to actually hit the animal at 10 yards. The heaviest, fastest, meanest arrow still sucks if you put it 6 inches over the animal's back.