How big of an animal can your bow kill? As more and more women and youth begin to take up bowhunting, the question regarding the amount of arrow energy that is being used is important. Each year, technology improves when it comes to bowhunting equipment. It is getting more efficient and capable of packing more energy without as much length and weight. However, is it too much to ask for a 40-pound bow that is drawn to only about 25 inches, even when there is a 100-pound whitetail in front of you? Is your existing whitetail bow ready to tackle elk hunting? Or what about elephant or Cape buffalo?
Kinetic energy is equal to velocity squared, which is multiplied by mass, and then divided by 450,240. The sum equals kinetic energy of a specific object that is in motion. This is how most bowhunters will determine the amount of arrow energy that can be used, but what exactly will these numbers tell you? Not much if you ask some people.
There are a number of issues with KE, when it comes to killing potential. First and foremost, these numbers are generally grained at what is known as “muzzle velocity,” which is directly off the rest of the arrow. It is a measurement of usable energy at any given moment, though it essentially doesn’t give you any information as to how the arrows will perform downrange. Drag that is created by atmospheric friction and fletching tends to lose initial energy pretty quickly. So, in other words, kinetic energy off the blocks does not precisely reflect energy that is usable on target 20 to 60 yards away. It also does not tell you a thing about how well a specific projectile will be able to perform once it meets living flesh.
In the KE formula, velocity is squared, which means that KE numbers can significantly increase as a result of relatively small boosts in speed. However, lightweight and fast arrows tend to lose initial energy at a much more rapid pace than heavier weight arrows traveling at a slower speed. When it comes to increasing speed, it typically means that you will need to lose arrow/point weight, which can directly impact the projectile reliability. In addition, the quicker an object is able to impact the target, the better the drag during penetration of a specific medium.
Many people think that kinetic energy is insignificant to bowhunters and are unable to fathom why people use it. It can be beneficial when it comes to side-by-side comparisons, but it is unable to reveal anything regarding performance potential in the real world. A more useful and accurate indicator of accessible energy is momentum, which is equal to mass times velocity. While this is more telling than kinetic energy, there are still some gaps overall.
With that being said, every bow hunt isn’t about penetration. While speed definitely holds some merit, since it seems the lightest-boned and thinnest-skinned animals are typically the ones that are the most problematic to approach closeup and are also most vulnerable to string-jumping—Coues whitetail and pronghorn, for example. With the likely scenarios, it will come down to balancing the equipment.
There are various additional elements apart from KE and momentum that can play a role in direct penetration.
Wide-cutting diameters tend to use energy cutting rather than driving forward. Cut-on-contact heads or cutting-tip designs often slide through the muscle tissue and split the bone more effectively than faceted pyramid or cone tips.
When determining the equipment that you will use on your hunt, you should consider the tenacity and size of the game that you are pursuing, probable conditions that will be faced, and predominant ranges that are anticipated. Yet again, there are compromises involved with the choice of equipment. If you gain in one area, it will mean that you sacrifice in another. An example would be to get the deepest penetration would mean that you would have the flattest trajectory.
Lightweight arrows (roughly 6.5 to 8 gains per inch), 85- to 100-grain broadheads, and mechanical broadheads do indeed have a place where they belong, particularly on small, delicate game that are bowhunted often. An obvious example would be turkeys, as recovering them after being hit often relies on flattening the turkey right there on the spot.
If you combine small crucial areas with long range shooting, then you can essentially create a solid case for mechanical broadheads. Penetration should not be a problem on such game with average equipment.
Game like moose and elk are what sparks the serious debates around penetration. Animals like these have extremely thick hide as well as durable bones, which are able to stop broadheads that are poorly made. Just as you are able to kill whitetails with a .22 Hornet cleanly, you can use light arrows and wide-cutting mechanicals to kill elk, as long as everything goes according to plan. When it comes to bigger animals, you may run into a worse-case scenario. In these instances, you will want tough, cutting-tip broadheads that lead the way as well as heavy arrows that can withstand significant abuse while driving broadheads home regardless of quartering angles and bone impact.
Heavy refers to shafts within the 12 to 15 gpi class as well as broadheads from about 125 to 145 grains. Ultimately, the goal is to increase strength as well as F.O.C. percentages so that the forward weight drags the trailing arrow through the massive flesh and bone. Rather than typical percentiles in the higher single digits, you should focus on obtaining numbers between 12 and 15 percent.
Ideal may be a 450- to 500-grain finished arrow with 14 percent F.O.C., pushed to about 260 feet per second.
Most people will be between the extremes, and keep in mind there isn’t a thing as overkill. When it comes to shooting an elk arrow, you will probably have a quieter bow, but compromising for the middle ground will permit ample penetration potential and versatility to confidently being able to “thread the needle” on some of the trickier brush shots or stretch the range a bit when a buck is reading across the meadow. Currently, 75 percent of the industry shafts offered are arrows between 8.5 and 10 gpi range with a 100- to 125-grain head.
At one time, ingenuity was involved in the assembly of perilous game arrows, which included stuffing one arrow in another arrow so that the proper weight was created or gluing steel inserts into standard broadheads to help reinforce forward mass. As previously mentioned, slower-moving objects that are heavier will better be able to retain their momentum than faster-moving objects that are lighter weight.
In today’s day and age, assembling an incredibly heavy arrow has gotten easier. Many manufacturers provide special shafts while keeping big game in mind, and these shafts have finished weights of between 650 and 850 grains. Some common examples include Easton’s Dangerous Game FMJ, Alaska Bowhunting Supply’s continuous-taper GrizzlyStik Safari, Gold Tip’s 100+ Big Game, and Carbon Force/PSE’s Black Mamba. Broadheads that weigh between 190 to over 300 grains are included with these—ABS and Steel Force offer several different extra-heavy broadhead options—to create 19 or higher F.O.C. percentage.
Any time that big and dangerous game is part of the mix, you should be looking for at least 650-grain finished arrow weight and 19 percent F.O.C. that is delivered between 200 and 225 fps. Of course, anything more is great as well.
The last 20 or so years has been spent by Dr. Ed Ashby studying various aspects that impact the penetration of arrows on game animals, utilizing already-dead animals. This started in Africa—and lately the Australian water buffalo—as test mediums for arrow and broadhead combinations. The most interesting of his findings are the extreme F.O.C. as it relates to penetration. Ashby’s tests demonstrate that high F.O.C. percentages offer a decisive edge when it comes to penetration on the largest game and most durable bone. By using arrows that weight over 650 grains, you can create higher F.O.C. with a single-beveled and solid broadhead. Dr. Ashby showed that even standard bow setups are more than capable of soaring right through the sturdy ribs of a water buffalo.
More importantly, these studies have paved the way for better comprehension of how compound shooters are able to ply below-average KE—youth, women, and elderly bowhunters own short draw lengths or tend to pull low draw weight—and achieve increased penetration through improved F.O.C. This includes 45- to 65-pound draw weight gear, since recurve and even longbows aren’t able to touch light-pulling compound bows for the transfer of energy.
Traditional thinking has held for some time that kinetically challenged archers opt for lightweight broadheads to match or exceed shorter and lighter arrows. Ashby’s studies show the differing information is actually true. Selecting a cut-on-contact, in addition to a heavier head, can sacrifice some speed, but it will also provide increased penetration potential that shooters require to succeed for larger game animals.
The above information is simply food for thought. It’s great if your current setup is having no problem penetrating game. However, if you are losing some animals because the penetration just isn’t there, then you quite obviously need to consider a new approach. The aforementioned information can help minimize wound loss, which is something that the animals you bow hunt deserve.
For more information, get in touch with us at Full Draw Archery.
Like this article