Arrow Energy: Are You Packing Enough Punch For Trophy Bucks?
September 22, 2011
Want to start an argument among whitetail hunters? Mention arrow energy minimums pertaining to big game hunting.
There's plenty of misinformation regarding this arrow energy, but the real dilemma is posed by determining how much arrow energy is enough to cleanly dispatch the trophy whitetail bucks about which we all dream -- using the specific outfit with which you bowhunt under "normal" conditions.
The debate is further complicated by youth and female bowhunters, who are likely drawing less weight and shorter lengths. Modern bowhunting equipment is becoming increasingly efficient, but is a 40-pound bow drawn to, say, 25 inches producing enough energy to cleanly and quickly dispatch even a 100-pound doe?
Just as importantly, is your whitetail rig up to snuff on the most demanding shots?
BY THE NUMBERS
Measuring kinetic energy is how most bowhunters determine an arrow's killing potential. The number is arrived at by multiplying speed squared by arrow mass and dividing the resulting figure by 250,240. But what do these numbers actually reveal? In my opinion, not much.
KE is a measurement of available energy at a given moment -- usually at arrow launch -- and is heavily weighted by speed. These "muzzle velocity" arrow speeds are highly misleading, as fletching and atmospheric drag diminish arrow speed considerably beyond 15, 30 or 45 yards. Likewise, KE reveals nothing of how a given broadhead design performs on living deer. After all, successful performance is about driving your arrow through vital organs, regardless of how an arrow meets its target.
Lightweight, fast arrows can produce inflated KE numbers at launch, but they also shed energy faster than heavier, slower arrows, especially after encountering resistance such as flesh and bone. Think in terms of a Wiffle ball verses a baseball for an exaggerated example.
Arrow speed can also be gained by decreasing arrow or field point weight (add 5 to 7 fps for every 25 grains shed), directly affecting projectile reliability.
Speed certainly holds merit, most notably in spot-and-stalk scenarios where ranges stretch. But for the average tree stand bowhunter, the speed advantage can actually prove a liability in that faster arrows normally result in noisier equipment. No matter what the "experts" say, you can't beat a whitetail to the jump. A fast arrow travels around 300 fps, but sound travels at about 1,225 fps. And whitetail's reaction time is measured in milliseconds. In the end, creating an "ideal" is about balancing equipment to likely conditions.
MORE THAN MEETS THE EYE
Penetration is a tricky subject. Aside from well-tuned bow and arrow combinations delivering missiles straight and clean -- more efficiently retaining energy en route and after impact with deer -- arrow material is also part of the equation. Carbon penetrates better simply because it recovers from launch and impact flex faster than other alternatives.
Despite arrow construction, broadhead geometry more directly affects penetration. Mechanical broadheads characterized by moving parts -- and especially aggressive cutting diameters and/or attack angles -- require more energy to penetrate deeply than streamlined fixed-blade designs. Certainly there are newer mechanical designs providing amazing efficiency, but energy transferred from one object to another (as in blade deployment) is lost to overall penetration. The least efficient mechanical designs sacrifice up to 20 percent of energy available for penetration. In most cases, we have energy to burn, and wider wound channels are worth the tradeoff when this is true. But take note: two holes are always better than one! If you're not seeing pass-through penetration on whitetails, perhaps it's time to look to a more efficient cutting-tip broadhead.
STRIKING A BALANCE
Small vital areas combined with longer ranges encountered while spot-and-stalk hunting for Coues whitetails make mechanical broadheads an easy choice. The same can be said in regions where 100-pound whitetails are considered the norm or difficult trailing conditions like tight vegetation or persistently wet weather rein. With "average" equipment (60- to 70-pound draw weight combined with a 28- to 29-inch draw length), penetration should prove more than ample.
Light arrows equate to flat trajectory and more margin for error on longer shots or while "threading the needle" in thronged vegetation. What this might look like is a 350- to 400-grain finished arrow with a minimum 9 percent F.O.C. (for stability's sake), pushed at about 300 fps (+/-10 fps).
On the other hand, bowhunting for big-bodied Midwestern whitetails changes the rules. Bigger antlers and colder weather also lead to an increased incidence of less-than-perfect shot placement. "Worst case scenario" is more likely in this context.
When bucks pushing the 200-pound mark are likely, hunters are well-advised to select a heavy arrow and a tough, cut-on-contact broadhead designed to stand up to abuse. This calls for shafts weighing 11-14 gpi and heads from 125-145 grains. This has everything to do with increasing penetration potential, as well as beefing up your Front Of Center (FOC) percentages.
High FOC literally drags trailing arrows through bone and massive muscle, but it also makes for a highly stable missile more likely to stay the course when a small twig or leaf deflects an arrow. This means boosting FOC to 12 to 15 percent -- 15 to 20 percent with traditional gear.
You can determine F.O.C. by finding measured center of the arrow shaft and the balance point with the broadhead installed. Measure the distance between these marks and divide by the overall arrow shaft length from nock throat to cut-off. Convert to a percentile by moving decimal point two spaces right. "Ideal" could be considered a 450- to 500-grain finished arrow with 13 percent FOC, pushed to about 260 fps (+/-10 fps).
But you say, "I don't take risky shots. I seldom shoot at anything outside 30 yards." Once again, shooting heavy arrows promises quieter shots. In concession, I'll also agree a middle-ground compromise allows ample penetration potential combined with versatility to confidently "thread the needle" on tricky brush shots, or stretch range a bit when a buck stands on open agricultural ground. This points to 8.5 to 10 gpi arrows tipped with a 125-grain head (or 100-grain granted FOC is doesn't dip below 12 percent).
The most confusion seems to stem from setting up "kinetically-challenged" bowhunters -- those with short draw lengths or low draw weight, say, bows producing less than 40 foot pounds of KE. The intuitive approach -- shooting the lightest arrow possible, combined with heads in the 75- to 85-grain class -- does not prove the best approach.
The slow-but-sure approach normally yields better results, choosing shafts "heavy" relative to deflection, like Carbon Express' Pile Driver (9.7 gpi) or Easton's Axis (9 gpi), instead of Blue Streak (7.4 gpi) or FlatLine (7.4 gpi) in 250 or 400, for instance, while also boosting FOC with 100- or 125-grain heads instead of 75- or 85-grain models. Sure, they travel slower, but they get the job done once on target. This approach also best serves traditional gear shooters wielding average draw weight (45 to 65 pounds), as recurve and longbows can't touch even moderate compounds for energy delivery.
I always cringe when reading dogmatic statements regarding bowhunting setup. Inasmuch, accept this information as food for thought. If your current rig's blasting through every deer you shoot, leave it alone. Conversely, if you've lost a deer due to lack of penetration or terminal-tackle failure, it's obviously time to make adjustments to your setup.