November 04, 2010
The Adventuresome Bowman takes a look at Dr. Ed Ashby's system for maximum arrow penetration on magnum game.
A protracted pointblank standoff with my first Asiatic water buffalo provided ample opportunity to study my formidable quarry, a small moun-tain of thick hide, muscle, and bone. When the bull spun and ran after the shot, I was overjoyed to see part of my shaft protruding from the far side of his chest before he collapsed in sight, 70 yards away.
No secret to traditional bowhunters, Dr. Ed Ashby's ingredients for the perfect bone-busting arrow are based on his years of penetration studies targeting oversized big game animals like Asiatic water buffalo.
The following year I shot another bull while helping my good friend, the late Bill Baker, develop his remote Australian buffalo camp. That arrow centered a rib on the way in, nicked a rib on the way out, and broke through on the other side for another lightning-quick kill.
Recovering from neck surgery that year, I was shooting a 78-pound recurve, and since I saw no need to fix what wasn't broken, I used the same bow on my second buff. Many authorities would regard that poundage as light for the quarry, and I would have had trouble talking an African PH into letting me hunt Cape buffalo with that setup, even though the body structure of the two animals doesn't differ significantly.
But I'd been paying attention to information from an ongoing arrow-penetration study that helped me compensate for my inability to handle the 86-pound recurve I'd been shooting before my surgery. Although I didn't have all the details, I did apply several of the study's key principles to my arrow-building. I shot sturdy, carefully honed two-blade broadheads. My finished Brazilian walnut shafts came in at just under 1,100 grains. And I coated my broadheads and shafts with a thin layer of lubricant before slipping them into my quiver. The source of the info that led me to those decisions: Dr. Ed Ashby.
Dr. Ashby, born in Texas in 1945, has bowhunted most of his life. After a career as a military physician specializing in diseases of the eye, he semi-retired to Africa to hunt and guide. In the 1980's he was invited to join a study conducted by the game department in South Africa's Natal province to determine whether heavy, dangerous game could be taken ethically and safely with archery equipment.
In the course of the Natal Study, Dr. Ashby conducted comparative examinations of arrow systems: broadheads, shafts, and hardware. The initial study involved many species of African wildlife. Later, Dr. Ashby focused on Cape buffalo as the definitive arrow-lethality challenge.
Alas, most shafts, heads, and hardware tested did not perform well. In a typical test round, Dr. Ashby would either kill a buff or accompany other hunters who did the shooting. With the buff still warm and whole, his team would arrange the carcass upright in order to allow shooting at realistic angles. Typically, Dr. Ashby took multiple shots with a variety of arrow setups from 70-80 pound traditional and compound bows. He would then study the carcass and take detailed notes and photos.
From the early Natal Study, Dr. Ashby formed his first opinions regarding what he considers the essential ingredients for a reliable arrow system: (1) structural integrity throughout, (2) as much arrow weight as an archer can shoot accurately, and (3) a solid single-blade (two-edged) broadhead.
That was the beginning. As the political situation deteriorated in Zimbabwe, where Dr. Ashby lived at the time, he moved to Australia where his arrow-penetration study continues today. For Dr. Ashby, Asiatic water buffalo have replaced Cape buffalo as test subjects. And as his years of study have grown into decades, Dr. Ashby's list of perfect-arrow ingredients and his personal philosophy on arrows have grown into the "Ashby System."
A young Dr. Ed Ashby began his arrow penetration studies many years ago while living in Africa.
As a matter of fact, his system has inspired a number of broadhead and shaft manufacturers to offer an array of Ashby-style heads. STOS offers a Tanto point, Eclipse and Zwickey are producing single-bevel heads, and Alaska Bowhunting Supply's "Ashby" broadhead flattens the scale at 315 grains, plus adaptor -- in effect, an armor-piercing chunk of 58-Rockwell bone-busting steel. Other manufacturers of both screw-in and glue-on heads are following suit.
But why should we care? "Heavy arrows for heavy game" is age-old wisdom and bowhunters after elk, moose, or grizzlies can certainly benefit from some of Dr. Ashby's principles, especially when shooting heavy bows that can push the weight. But for the average whitetail hunter shooting medium-weight bows, isn't this overkill? Not to Dr. Ashby, who doesn't believe there's such a thing as over-built arrows or overkill.
What has motivated Dr. Ashby from the beginning is still what drives him today -- his desire to decrease wounding loss and increase hunter success. No losers. From his point of view, bone hits are inevitable. Bowhunters shooting light setups risk losing animals.
No winners. Ashby's studies suggest that the old wisdom -- any sort of bow and arrow setup can kill anything with a well-placed arrow and sharp broadhead -- reflects wishful thinking. Moreover, Ashby has recently added a 54-pound longbow to his standard arsenal of heavier test bows and learned that the lighter the bow, the greater the percentage of penetration gained by following his formula for a perfect huntingarrow.
According to Dr. Ashby's work, the following 10 points describe an arrow system designed to enhance penetration and promote fast, humane kills on big game, especially in the case of bone hits. (Editor's Note: The author prepared the following synopsis with the help of Colorado bowhunter and journalist Dave Petersen, who has extensive familiarity with Dr. Ashby's arrow-penetration studies. The resulting recommendations are Ashby's opinions based on his reported findings as they relate to arrow penetration on magnum big-game animals like buffalo. We leave it to our readers to decide what elements of the system work for them and the big game animals they pursue.)
1. Structural Integrity describes an arrow's ability to hold together on impact, even with heavy-bone hits, and is the most important factor in arrow system design, applicable all the way from broadhead tip to nock. According to Dr. Ashby's findings, even a tiny broadhead tip bend results in an average penetration loss of 14 percent.
A. Strongest Broadhe
ads (with variations due to construction design, thickness, hardness, and type of steel) are generally fixed single-blade (two-edged), followed by fixed multi-blade heads, component (replaceable- blade) heads, and mechanicals.
B. Strongest Shafts rank from hardwoods like Forgewood, hickory, lam birch, purple heart, and ipe (Brazilian walnut); to aluminum and carbon; to softwoods like cedar, Scotch pine, and Hexwood.
C. Strongest Hardware materials are steel and brass.
D. Aluminum Inserts can be a weak link when used with screw-in heads.
E. Aluminum Broadhead Adaptors may be the weakest link in carbon and aluminum arrow systems.
2. Perfect Arrow Flight is necessary to deliver maximum usable force to the target and permit other factors to work at full efficiency. Poor flight squanders arrow force.
3. Extreme Forward-of-Center (EFOC) Arrow Balance. Except for perfect arrow flight, proper FOC -- how far forward of shaft midpoint an arrow balances across a finger -- contributes more than any other element to maximizing penetration. The Ashby studies favor EFOC: 20 percent or greater, measured using the ATA standard method.
Dr. Ed Ashby has used the carcasses of freshly killed Cape and Asiatic buffalo to test different styles of arrows and broadheads. From this testing, he has compiled criteria he believes will assure maximum arrow penetration on magnum animals.
Thanks to the growing menu of heavy screw-in hardware and internal inserts, EFOC is most easily attained with carbon and aluminum shafts. But even without EFOC, if a woody shooter maximizes the other arrow-efficiency factors discussed here, average penetration reportedly will be more than double that produced by an identical arrow lacking these features.
For his FOC testing, Dr. Ashby used 82, 70, and 54-pound bows of similar efficiency. On average, the 54-pound bow's EFOC arrows out-penetrated the 82-pounder's standard arrows by 48.8 percent!
4. Broadhead Mechanical Advantage (MA) has a more pronounced influence on the penetration of a perfectly flying, structurally sound arrow than any other factor except EFOC. Its advantage is applicable to arrows of all designs. However, the more efficient the overall arrow, the more penetration gain a high-MA broadhead will yield. Among the characteristics of mechanical advantage are head profile (on a two-edged head, a length-to-width ratio of 3:1 is ideal), ferrule profile (smooth and aerodynamic ferrules perform best), and number of blades. (Among the most significant findings in the early Natal
Study was that almost all rigid, single-blade broadheads out-penetrate almost all multi-blade heads. Decades of subsequent penetration testing confirm the advantage of a well-built and designed two-edged head.)
5. Shaft Diameter to Ferrule Diameter Ratio. An average 10 percent more penetration derived when an arrow's shaft was at least 5 percent smaller than the broadhead's ferrule diameter, compared to shafts and ferrules having equal diameters. When shaft diameter exceeded ferrule diameter, penetration decreased by an average of 30 percent compared to systems having equal diameters.
6. Arrow Mass. While a physicist might bicker, for these purposes it's safe to think of mass as weight. Lower-mass arrows use their force less productively because they have less "useful momentum." More of their momentum is represented by speed and less by arrow mass/weight. Arrow velocity decays rapidly during penetration, but mass, embodied in the arrow itself, remains constant. In short, heavier arrows take longer to stop.
Since bone impacts of some type occur on most game hits (remember, ribs are bone), Dr. Ashby personally will not hunt any big game animal with an arrow whose overall weight falls below a minimum bone-splitting threshold that his research has established as 650 grains. Every bit of mass above that threshold enhances penetration gain, as long as increased arrow weight doesn't impact shooter accuracy or quality of arrow flight.
7. A Scalpel-Sharp Broadhead is of prime importance in penetrating fibrous tissues. With all other factors equal, super-sharp heads show a 26-percent average gain over smoothly filed but "merely sharp" heads, and more than a 60-percent advantage over "Hill-type" serrated edges.
8. Arrow System Profile and Finish. Thinner shafts penetrate better than thicker shafts. Single-taper shafts show an 8-percent penetration advantage over straight shafts, and 15 percent over barrel-tapered shafts. Even parallel shafts show a 7-percent advantage over barrel-tapered shafts. Slickness counts too. While rough or irregular surfaces increase arrow drag in all tissues, the loss is greatest through bone. The less "bumpy" an arrow's overall silhouette, the more easily it passes through tissue. Teflon-coated heads average 12 percent more penetration on soft tissue hits.
9. Type of Edge Bevel. When broadheads identical in every way except edge bevel are mounted on identical shafts and shot with the same bow(s) into identical tissue, single-bevel heads demonstrate sizable penetration increases in all cases involving bone impact.
The gain varies by broadhead profile but ranges from 14 to 58 percent. The thinner edge of a single-bevel slices deeper at any given level of tissue tension. Additionally, a lower and longer bevel means higher MA for the cutting edge, slicing better at the same force.
The biggest advantage is the rotation single bevels induce during penetration, helping to split bone rather than merely "pushing through." An arrow that twists its way through soft tissues produces a much longer cut channel. Finally, if the arrow is still rotating when it exits, the taut skin can catch up and twist tight as the blade slices through, creating a large, distinctive, L-shaped exit wound.
To avoid losing penetration, however, it's essential to match blade and fletching angles: right to right, left to left.
10. Broadhead Tip Design. The greatest importance of tip design comes on shots impacting bone. The Tanto tip shows the best overall performance and lowest damage rate of any design tested, both on single and double-beveled blades. Moreover, of all common tip profiles, the Tanto demonstrates the lowest tendency to skid off bone during angular impact.
Summary and Recommendations:
- Strong from broadhead tip to nock, with steel or brass hardware.
- Perfect arrow flight.
- Heavy overall arrow system, with extreme or at least high FOC balance.
- Single-taper, slender, no larger than ferrule.
- Smooth, preferably slick finish.
- Tough: hardwoods, aluminum and carbon, and softwoods in that
- Fixed single-blades (two-edged).
- Strong, with high MA.
- 3:1 body taper.
- Single-bevel edges.
- Tanto tip.
- Aerodynamic silhouette.
Full disclosure: I haven't adopted all 10 of these principles in my own bowhunting arsenal yet, although I'm looking at those I have yet to bring into play. Those choices reflect both my own inertia and what I consider healthy skepticism derived from my own scientific background. But during decades of fireside discussion, I've listened to countless opinions concerning optimal arrow design, most of which contained more conviction than evidence.
Dr. Ashby's studies provide rare insights in that he has at least attempted to apply scientific principles to questions that have confounded bowhunters for thousands of years, and for that we should all be grateful. To learn more, you can check out Dr. Ashby's reports and updates on permanent file at www.tradgang.com.
Adventuresome Bowman Don Thomas lives with his wife, Lori, in Montana.