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Arrow Penetration Qualities

 
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Old 10-14-2012, 08:18 PM
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Arrow Penetration Qualities

I felt compelled to compose this missive this after receiving a weekly “tech tip” from an archery only web-site containing the prominent statement of: “Shooting a heavier arrow (shaft + tip) will not necessarily give you more penetration (kinetic energy) over a lighter arrow. Check it for yourself ... take your bow and shoot a heavy arrow and a light arrow through a chronograph, then calculate the kinetic energy. I bet the values aren't much different.”

So much sales hype circulates in the archery market touting arrow speed and really very little discussion time is spent on, what I have come to believe is, the more critical topic of actually killing game. After all, the vast majority of shekels spent in the archery industry are dedicated to deer hunting. Being able to hit a target at range, accurately is important; however, if the pursuit revolves around the ethical killing of game, hitting and killing are not actually the same topics.

Please bear with me if you’ve heard this all before.


An arrow’s penetration (or lack thereof) is based on a number of variables.
The current rage in archery advertisement centers on velocity. From a simple calculation using an arrow’s weight and it’s velocity at impact a number, kinetic energy (k.e. commonly a measurement in foot pounds) can be obtained. Basing conclusions about an arrow’s ability to penetrate solely upon velocity, k.e. or a combination of both can be misleading and even cruel. If one were to base his decision on using a particular set up based just on k.e. he is missing large parts of the equation.

Killing with an arrow has little to do with actual energy transferred to the target as is commonly found in the firearms industry. If one stops to think about it, were the arrow to actually drop all of its retained energy into the target at point of impact, the arrow would not penetrate at all (as in the case of a small game “blunt” type arrow). An arrow actually performs better when less of its retained energy is shed in the target and penetration is affected by the slicing action provided by a well designed broadhead that maintains its shape and sharpness while performing its primary duties of destroying the vital circulatory and/or respiratory systems.

One of the most overlooked factors in arrow choice for maximizing penetration is inertia. Inertia is a body’s propensity to maintain speed and direction based primarily upon its mass. Yes, it takes more energy to start a massive projectile moving but it also requires more effort to change its direction or to stop that travel. In other words: We absolutely want that broadhead to penetrate as far as possible into and beyond (if possible) the target. The arrow’s “impact” has little or nothing to do with its intended purpose.

More massive projectiles may or may not strike with more kinetic energy but they tend to retain more of their initial velocity while in flight and during encounters with the target.


Penetration is also affected by:
  • Diameter of the shaft (smaller diameter equals less resistance and greater penetration)
  • Number and angle of cutting edges of broadhead (i.e. a more gradual angle to the cutting edge provides less resistance and better penetration and two cutting edges require less energy to cut than three edges, three edges require less than four edges)
  • Smooth transition from broadhead ferrule to arrow shaft promotes penetration (a larger ferrule with smaller O. D. shaft penetrates better than same sized shaft and ferrule while a larger shaft than ferrule penetrates more poorly than either of the above)
  • Stiffer shaft penetrates better than a more flexible shaft (less energy is consumed in shaft flexing after impact and more is retained for forward movement)
Of course, taking any one of the factors outlined above to an extreme (i.e. very heavy shaft but too slow to even find the target) does our goal of successfully harvesting game no good.
My admonition to everyone is to be aware of the decisions you are making when choosing an arrow/bow combination. Be careful to filter the advertising propaganda possibly spread by the counter salesperson from the physics of what you actually need to do. There is no free lunch and the current focus on speed and kinetic energy as the end-all be-all to our archery problems is short sighted. While desirable for the 3-D course, that intense commercial focus on speed alone has actually produced a dramatically increased level of struck and wounded game escaping because of inadequate penetration. Merely being able to hit our target is insufficient if we can not reliably bring our intended quarry to ground in an ethical and humanely quick fashion.

Not to put too fine a point on it (all puns aside) but the broadhead needs to make it all the way through those vitals and hopefully out the other side producing a wound channel that allows maximum loss of vital fluids and/or gasses. On deer that can be reliably done at 200 feet per second at 20 yards with a sharp broadhead and stiff, heavy arrow every time the mark is hit.

Hitting a foam target is not the same as hitting one of God's creatures.
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“The rifle itself has no moral stature, since it has no will of its own. Naturally, it may be used by evil men for evil purposes, but there are more good men than evil, and while the latter can not be persuaded to the path of righteousness by propaganda, they can certainly be corrected by good men with rifles.”

Col. Jeff Cooper
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  #2  
Old 12-19-2012, 07:08 PM
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Re: Arrow Penetration Qualities

I agree with everything in a perfect world. Only thing I would take objection with is the stiffer arrow comment. I matched arrow (spine) to the set up and correcty tuned equipment will out penetrate a arrow that is over spined (stiffer) for the setup. If a arrow is under spined the transfer is energy is to great resulting in loss energy in the arrow from over flexing, if arrow is over spined the energy loss will be in the bow resulting in not enough arrow flex. The transfer of energy and resulting flex in the arrow as it travels down range is know as archers paradox.
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  #3  
Old 12-19-2012, 07:20 PM
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Join Date: Dec 2007
Location: Gila Wilderness,New Mexico
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Re: Arrow Penetration Qualities

I call it "Chasing Sexy" many people want fast speeds at all costs... Even at the cost of Momentum..

J
The New Mexico Sportsman
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  #4  
Old 12-19-2012, 08:35 PM
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Re: Arrow Penetration Qualities

I use nothing but fixed blade broadheads and keep it under what I think is the magic number of 280fps. For whatever reason, above that speed every bow I have owned gets touchy in its tuning and slight form breaks. Anyone can have good form when standing at a stake or firing line, but while hunting it gets rather difficult requiring an animal wait for me while looking for a level spot to get a shot.
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  #5  
Old 12-20-2012, 04:59 AM
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Re: Arrow Penetration Qualities

Konrad,

I agreee with a lot of what you put up, and don't disagree with any of it. Your right there is a theme today which seems to be shoot as fast as I can, and the rest will take care of it's self. I have seen plenty of hunting shows where the arrow will hit the animal and not penetrate more than a foot at the most and the hunters are gong crazy with high fives and such on how good a shot it was. Me personally I want to have to pull my arrow out of the ground or the trees behind what I shot and know fo sure and certain there is a double wide hole in both sides.

I got into archery as somewhat of a "you need to try this out" by my good friend and hunting bud. They have hunted this way for years, and he had gotten away form it and started back up a few years back. Well I wasn't ovelry impressed with it but eventually I was talked into it. The year prior to me buying my first bow, my frind had been on a huge buck hot and heavy. He hunted every chance he got during archery season and even took his bow out the opening weekend of rifle season to try and get this monster. Well he got his chance, and at he shot the deer stepped sideways, and it resulted in the arrow hitting right in the shoulder socket. Penetration was only about 1-2" at most, and the buck quickly broke the arrow off on the nearest tree as he left the area. Two year later, the buck was still going and still putting out his best on the does but none of us ever got another shot at him.

That said my bud was sick, and threw out everything he had been working with and went to work on his equipment. He got into Dr. Ashby's writings, and along with the newer arrows and broadheads on the market, he put together about the best combination for our type hunting that he could have.

He can't draw but 65# at most, so that limits him somewhat to stick within a certain range of arrow weight and still get a bit of speed. Like you mentioned however when we went at this we didn't go looking to break 300fps, but to have the best weight moving at the best speed with the best broadheads up front on the smallest diameter shaft.

So what we ended up with were the Axis FMJ, small diameter, smooth sturdy shafts, and plenty of weight to them to ensure penetration once they got on target. From there we probably spent $1K easily on different broadheads to determine what would penetrate best on the ends of these shafts, at the speeds we were shooting. Our final result was a 28 or in my case 29.5" FMJ 400 for him and 340 for me, Blazer vanes, and the 100 or 120gr Slick Trick Razor Tricks broadheads. With this combination we're getting 240 - 270fps from any of our bows, and nothing has stopped the first arrow yet. He set his wife up with the 500 FMJ, 27" and the same broadhead. She is only drawing 45#, and so far she has shot through every deer she has put them on.

Yes there is a LOT to say for having a good weight behind the shot, and not trying to rely on speed. The trouble with most today however is they want instant accuracy, and most who hit the field haven't a clue as to if their stuff is tuned up and dialed in or not. They just know they can hit a pie plate diameter area with the latest mechanical this that or the other and feel they will be cutting 5" of hole into something it has to drop. It might, but chances are greater it will leave a long trail which will probably not lead to their deer.

Since getting into archery, I now have three bows. All of them are great shooters, "IF" I practice. I can take any one of them at any time and hit an ear plug at 20yds within a dozen or so shots, but that doesn't mean I am ready to hit the woods. In fact I turned down several chances this year simply due to I haven't had time to practice. I know the bows are dialed in, as well as the arrows are matched to the bows, but I cannot reliably say that I am ready. I proved that this past weekend while shooting two of them. The muscle memory simply isn't there, nor is the consistent shot to shot accuracy. I hold myself to a higher tolerance, that if I cannot hit within an inch or less of my ear plug at every range out to 40yds I am not heading to the woods to try and kill a deer. I have to know in my mind that I am up to the challenge, just as I do with my rifles. IF they don't shoot 1" or less groups I don't use them in the woods.

Keep up the thought process you have going it will go far with your hunting. You are for sure on the right track. There are plenty of critters taken every year with all sorts of equipment. Some are exactly the way it should be, some aren't. Some folks will always strive to be, and use the best they can, while others simply get by. It is the same with firearms as well as any other means. It is the hunter that makes the differences.
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  #6  
Old 12-20-2012, 01:24 PM
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Join Date: Aug 2010
Location: North West Washington
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Re: Arrow Penetration Qualities

Hello Mike,

Thanks for the informative, thoughtful and well documented post.
I personally had not given much consideration to the subject of optimum penetration until I started reading Ed Ashby’s work and doing some limited experimentation on my own. The fact that the number of “hit and lost” deer in Ashby’s woods had dramatically increased since the acceptance of the compound bow was an alarm that should have rung in a lot of professionals’ ears (i.e. guides, wildlife biologists and managers).

For me, the penetration issue was a natural carry over from my firearms experience. The first modern rifle I ever purchased was in 375 H&H. I have since purchased other calibers and used them a field but I have always maintained a warm spot for my 375’s (they seem to multiply in my safe). I just seem to feel more confident with my Number 1 Tropical. Perhaps that comes from having used it the most or its inherent accuracy or that beautiful 300 grain spitzer boat tailed Sierra projectile or the fact that I have never needed another shot or had to track anything once hit with it. It comes back to the same two things, being able to accurately place the shot and leaving a second hole on the other side of the target.

Thanks again and Merry Christmas,
K
__________________
“The rifle itself has no moral stature, since it has no will of its own. Naturally, it may be used by evil men for evil purposes, but there are more good men than evil, and while the latter can not be persuaded to the path of righteousness by propaganda, they can certainly be corrected by good men with rifles.”

Col. Jeff Cooper
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  #7  
Old 12-20-2012, 01:42 PM
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Location: North West Washington
Posts: 80
Re: Arrow Penetration Qualities

Quote:
Originally Posted by sox35 View Post
I agree with everything in a perfect world. Only thing I would take objection with is the stiffer arrow comment. I matched arrow (spine) to the set up and correcty tuned equipment will out penetrate a arrow that is over spined (stiffer) for the setup. If a arrow is under spined the transfer is energy is to great resulting in loss energy in the arrow from over flexing, if arrow is over spined the energy loss will be in the bow resulting in not enough arrow flex. The transfer of energy and resulting flex in the arrow as it travels down range is know as archers paradox.
Hi,

I use Easton Technical sifts exclusively in my archery pursuits. For virtually every application Easton lists a number of shaft spines that will “work”. Sometimes the spine may only vary by a few thousandths of an inch and most launching platforms can be “tuned” or adjusted for optimal flight with any of the given spines within the reference chart. When I refer to using the stiffest shaft possible, I am referring to the stiffest shaft within the suggested range of spines for that application.

I am an aficionado of the alloy shaft exactly for that reason. One can choose exactly the spine required to achieve the most perfect flight available for any combination of draw length, draw weight and point weight. The current selection of carbon composite shafting is suggested for a much wider application spectrum. They say it will “work” and it does to one degree or another. I strive for the highest level of perfection that I can achieve. Sadly, that level is generally all too low so I need all the help I can get!
For one reason or another I always seem to wind up on the stiff end of the chart and when comparing apples to apples a stiffer shaft, of equal diameter, flying properly, will penetrate farther as more of the energy imparted to the shaft is used in forward motion rather than oscillation.

You do bring up valid points.
__________________
“The rifle itself has no moral stature, since it has no will of its own. Naturally, it may be used by evil men for evil purposes, but there are more good men than evil, and while the latter can not be persuaded to the path of righteousness by propaganda, they can certainly be corrected by good men with rifles.”

Col. Jeff Cooper
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