Compound Bow Selection
Guide
Help Chapters
1. Introduction
2. Keeping Things in
Perspective
3. Statistical Deception in
Advertising
4. Understanding Trade-Offs
5. What Makes Bows More "Powerful"
6.
Energy Storage and Release
7. Understanding IBO Speeds
8. Understanding the Force Draw
Curve
9. Theoretical Limits to
Performance
10. The Bow's Powerstroke
11. Brace Height - Effect on Velocity
12. Brace
Height - Speed vs. Forgiveness
13. Draw
Weight - Adjustability
14. Draw
Weight - Effect on Velocity
15. How Much Weight is Necessary
16. Kinetic Energy Basics
17. Kinetic Energy Testing & Results
18. Draw Weight - Our Recommendation
19. Draw Weight
- Super Human Strength
20. Understanding Let-Off
21. Pope & Young 65% Rule
22. Understanding the Valley
23. What Causes Hand-Shock
24. Causes of Vibration and Bow Noise
25. Controlling Unwanted Vibration
26. Solid Limbs vs.
27. Heavy vs. Lightweight Bow Designs
28. Axle-to-Axle Length
29. Single
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Introduction:
Like many products,
compound bows come in a variety of shapes, sizes, colors, and levels of
sophistication. If you’re new to the sport of archery, we’ll guide you
through all the jargon and technical hoopla and help you to make a
better-informed choice on your new bow. No advertising hype or sales pitches
here. |
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There are many
characteristics that archers look for in a new bow. Most archers want a bow
that has blazing fast performance, a silky smooth draw stroke, very low
hand-shock, a generous valley, and high let-off. Most archers also want their
bows to be very lightweight, compact, quiet, forgiving to any flaws in
technique, easy to tune, easy to adjust, and affordable for any budget.
Unfortunately, this perfect bow doesn’t exist. To get a bow with a certain
set of characteristics, you’ll likely have to sacrifice some others. For
example, very fast bows are generally less forgiving. Very light bows are
generally more expensive, and so on. Ultimately you’ll have to decide which
characteristics are most important to you and choose the bow that best fits
your personal criteria. |
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When you pull the string
of a compound bow, the limbs of the bow are squeezed inward. The energy you
supplied to draw the bow is stored in the limbs, as potential energy, until
you release the string. Upon release, the potential energy is transferred
into the arrow as kinetic energy, as the limbs "spring" back into
place returning the string to it’s original
position. Seems simple enough! But careful examination of this process of storing
and releasing energy is what gives a compound bow its performance
characteristics, and it is something you should consider when selecting your
new bow. The Point: In essence, there are only two factors that
determine how much "power" your bow will have: 1) The amount of
energy that can be stored in the limbs during the drawstroke. 2) The amount
of that potential energy that can be successfully transferred into the arrow
upon release (efficiency). |
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Area Under the Curve
(no calculus required): The Force Draw Curve
(above) represents an average modern single-cam compound bow. The amount of
energy the bow stores is represented by the darkened gray area under the
curve. The more gray area you have, the faster the
bow will shoot. So how do we get more gray area? Just change the shape
of the curve. Of course, changing the shape of the curve requires
changing the bow's major characteristics. This is where draw length,
draw weight, cam design, let-off, brace height, and other attributes come
into play. If you're looking for a fast bow, energy storage is what it's
all about. |
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If speed were the only goal,
a Force Draw Curve shaped like this one (at
left) would yield the greatest possible amount of stored energy for any bow
at 70# max draw weight and 30" draw length. Of course, a bow like
this would be nearly impossible to aim and shoot. With a 0" brace
height, the string would rest on the bow's handle, and would nearly chop off
your hand with every shot. And the bow would have no let-off, leaving
you to hold back the entire 70# until release. A bow like this would be
far more dangerous to the archer than it would be to the game animals.
And although this graph is only a theoretical example, it can help us to understand how today's super-cam bows are yielding
faster arrow speeds than ever before. But beware! The closer a bow's Force Draw Curve comes to the
theoretical limit graph, the more difficult it is to draw, shoot, and
control. |
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The curved line on the
force draw curve represents the bow’s drawstroke, commonly known as the
powerstroke. The powerstroke represents your effort. The
powerstroke begins as you pull the string back from the resting position and
is completed when the bow reaches full draw. Each bow will have a different
powerstroke depending upon its settings and cam characteristics. Powerstrokes which are longer, higher, or flatter will
generally result in increased energy storage and arrow velocity. |
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Draw Weight - Our Recommendations Before you choose the
draw weight of your new bowhunting rig, you should realize that you’ll need
to be able to draw your bow back quietly, slowly, and smoothly to avoid spooking
the game. When the time comes for that all important shot, you may be tired,
nervous, cold, hungry, cramped, and bundled up in multiple layers of
clothing. If you’re struggling to draw your bow back when just practicing in
your back yard or on your local 3D course, you risk disaster in the field.
Can you imagine missing a big buck opportunity because you lacked the
strength to draw your bow at that critical moment? It happens to countless
bowhunters every year, though most guys don’t freely admit it. An adult male
with average physical strength will be most comfortable with a 55-60# draw
weight. An adult female with average strength will be most comfortable with a
30-35# draw weight. If you are unsure about which limbs you should select for
your bow or feel you are "between sizes", we recommend you choose
the lighter limbs. |
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Draw Weight - Super Human Strength The truth is, many guys just can’t resist their "He-Man"
impulses to try to shoot heavyweight bows. If you’ve ever visited a busy
archery shop, you’ve certainly noticed guys who seem determined to prove
their super-human strength by yanking and jerking these 70+ pound bows until
they're on the verge of a hemorrhage. In spite of the strain, most guys will
still choose bows which have too much draw weight. Some compound bows are
available up to a 100# draw weight. While these bows will produce remarkable
penetration on a target, they will not necessary produce faster arrows speeds
or flatter trajectory. Since these bows must shoot arrows which are very
stiff and heavy, they rarely outperform their lower weight counterparts. A
100# bow will need to shoot at least a 500 grain arrow and will require very
high quality accessories to help dampen and withstand the heavy shock and
vibration the bow is likely to produce. This type of bow should only be used
for special purposes where huge amounts of kinetic energy
is necessary. Think carefully before ordering this type of bow. These
heavyweights are available by special order only. And since high draw weight
bows are easily dry fired, we do not accept returns on bows which have draw
weights in excess of 70#. |
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Many new bows are
available with high and low let-off options, primarily to keep Pope &
Young hopefuls within the rules. The Pope and Young Club is one of |
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The "V" shaped
area of the force draw curve is known as the valley. The shape of the
valley gives you some indication how quickly the bow lets-off at the end of
the drawstroke. Less aggressive cam and eccentric wheel designs have a
gradual drop off, letting-off over the course of several inches at the end of
the drawstroke. Aggressive cam bows often have a very abrupt drop-off,
where the let-off occurs at the last possible moment in the drawstroke (a
narrow valley). By delaying the let-off, additional energy can be
stored during the powerstroke to squeak out a few more fps.
Unfortunately, a narrow valley takes a little getting use to. When at
full-draw, you will notice that if you allow the string to creep forward
(just out of the valley), the bow will aggressively begin to yank
forward. Very aggressive cams can have valleys less than 1/4" at
full let-off. This can be troublesome, especially for high let-off shooters,
since the holding weight can abruptly change from 14 lbs to 70 lbs if you
allow the string to creep. Be prepared to make some moderate changes in
your shooting form if you elect to go with an aggressive cam bow. CAUTION: If you draw a high let-off bow
without an arrow on the string, make sure you have a firm grip. High
let-off bows are easily dry-fired. Once you draw the bow back and begin
to relax, holding only 12 or 15 lbs at full draw, you're likely to forget
that the full 70 lbs is waiting for you, just a 1/2" or so away.
When you begin to let the bow down, your grip is too relaxed, and
WHACK! DRY-FIRE! Dry firing a bow is not only dangerous to the
shooter, but it is an ideal way to seriously damage your expensive compound
bow and generally voids most manufacturer warranties. |
Wider Valley - Less Energy
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As compound bows have
become faster, storing more and more energy, manufacturers have increasingly
had to deal with the issue of hand-shock or "kick". Don't
confuse hand-shock with excess vibration. Vibration, felt in the handle
of a bow, is another issue. Hand-shock is caused when the bow jumps
forward or kicks up upon release. It's a natural byproduct of such an
explosive energy release, however much is made over this issue (perhaps too
much). A bow that produces no hand shock is like a car door that makes
a solid "thump" when slammed. While it may be the layman's
quick way of assessing a solidly built product, it has little real impact in
the performance of the machine. The goal of the compound bow is to
accurately launch an arrow into a target, not make your hand feel all warm
and fuzzy. There are many bows which are very quiet and accurate, yet
still have noticeable hand-shock. Only when hand-shock is truly
excessive, can it have a negative effect on accuracy and comfort. In
spite of all the industry hoo-hah about harmonics, riser materials, and
magic-cam systems, hand-shock is mainly a function of one thing. LIMB ANGLE.
When a bow is fired, the loaded limbs snap back into their original
positions. The inertia of the moving limbs causes
the bow's riser to jump (kick) in the same direction as the
limbs. Basically, if the limbs are positioned so that they jump forward
upon release, the riser jumps forward too. Since your hand is the only
thing that stops this forward motion, you feel the riser's movement as
hand-shock. But some bows are designed so the limbs are bent far over
(high static deflection), almost parallel with each other. When this
type of bow fires, the top limb jumps upward, the bottom limb jumps downward.
So the upward movement of the top limb cancels out the downward movement of
the bottom limb and the bow doesn't "kick". See the examples
(far left) of low-shock designs. Notice that the limbs on these bows
lean far back from the riser at a high angle of deflection. At full
draw, the limbs of these bow models will be practically parallel with each
other. If you are concerned about hand-shock, you should choose a limb
design that incorporates this type of high deflection limb angle.
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Cause
of Unwanted Vibration and Noise The last thing that a
bowhunter wants to sacrifice is stealth. A quiet bow can mean the
difference in filling your tag, or just telling the story of the one that got
away. In addition, a noisy bow is a sure sign that energy is being
wasted. Some bows tend to be quieter than others, depending upon their
designs. Before we can pick this issue apart, you should know a little
about the nature of sound. Vibration is what creates sound.
Without vibrations, there would be no sound. For example, when a guitar
string is picked, the string oscillates back and forth (vibrates), moving the
air that surrounds it, causing the tiny variations in air pressure that our
ears detect as sound. Some of those vibrations from the guitar string
also travel into the body of the guitar. If you've ever placed your
hand on a speaker or musical instrument, you've certainly noticed that you
can feel, as well as hear, the vibrations it creates. The same is true
for the compound bow. The rapid movement of the string and limbs
creates considerable vibrations when a bow is shot. The vibrations
exist because the string and limbs continue to oscillate back and forth
(vibrate) even after the shot is complete. If the vibrations can be
stopped quickly, before they have a chance to create sound, the result is a
quiet bow. If the vibrations are allowed to continue and die-out
naturally, the string will continue to "twang" and the limb
vibrations will transfer into the bow's riser and into the bow's
accessories. Not only does this create a 'buzzing" feeling in your
hand, the vibrations also cause any loose parts on
the bow to make noise. Incidentally, in many cases shooters blame a bow
for being noisy when in fact the accessories are the true noisemakers.
There is an easy way to test for accessory noise. Holding your bow in
your hand, take a small rubber mallet and gently tap the bow in a variety of
spots. You should hear only the "thud" made by the rubber
mallet. If you hear a "buzz", you have an accessory or
fastener that needs attention. A tube-aligned peep-sight is also a
common culprit for noise. The rubber tube often makes an alarming
"slap" when the bow is fired. However, your greatest
noise-maker on a bow is typically the string. There are plenty of
products to help silence your string (spiders, string leeches, whiskers,
etc.). Silencing a string usually isn't a problem. However,
stopping the limb vibration is a bit more difficult to accomplish. |
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Some manufacturers have
new designs that stop much of a bow's vibrations. Browning's
Sorbothane™ System, Bowtech's Sandtrap™ Limb Pockets, and PSE's NV System,
are all good examples of effective new vibration dampening systems for
2001. Designed to stop the bow's limbs from vibrating after the shot,
these systems prevent the transfer of vibrations into the bow's riser, for
quieter overall bow performance. Unfortunately, these systems are
typically offered only on the more expensive bow models. This isn't to
say that an archer on a budget can't have a quiet bow. With the
addition of inexpensive Limb Savers™, a high quality stabilizer, and a few
other cost-effective doo-dads, most modern compound bows can be quieted down
nicely. Don't be swayed by ads that claim a bow is "Quiet as a
Whisper" without backing it up with HOW that was accomplished. The
fact is, all bows create vibrations and noise. It's how the bow designers deal with the vibrations
that makes all the difference. |
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This is a tough one, but
it basically boils down to comparing six in one, and a half-dozen in
another. Some manufacturers like Bowtech, Browning, Martin
, PSE and a few others tend to design their bows to use solid
limbs. Other manufacturers like Alpine, High Country, Pearson, and
Reflex, mainly utilize split limb designs on their bows. A few
manufacturers even mix it up and offer both. Solid limb proponents
claim that solid limbs are more durable, offer better torsional stiffness,
and are more accurate than split limbs. Split limb proponents claim that split limb bows are lighter, faster, and
produce less hand-shock than solid limbs. While there may be some
marginal or theoretical evidence to support each of these positions, in the
real world, solid and split limb bows perform similarly. Whatever your
preference, limb type should be a minor consideration compared to the other
bow design characteristics we've discussed. Weigh this bow attribute
lightly. Beyond the aesthetic appeal, it probably doesn't matter, as
one type is likely to perform about as well as the other under most circumstances. |
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In response to the demand
for lighter and lighter compound bow designs, the average new compound bow
now weighs only 3.7 lbs (without accessories). Considerably lighter
than their recent predecessors, these lightweight designs are the result of
careful machining and high-tech lightweight materials. Modern bow
risers, which account for most of a bow's mass weight, are typically made
from aluminum or magnesium. But in order to save weight, many
manufacturers machine away excess metal from the risers and cams, giving them
a Swiss-cheese like appearance while still maintaining the structural
integrity of the parts. A few bows, like the Carbon Series by High
Country Archery, take a different approach, utilizing carbon fiber composites
instead of metal to construct their risers. Unfortunately, lightweight
bows come with a few drawbacks as well. To begin, most lightweight bow
designs are quite expensive, averaging $400 or more. You may also find
that lightweight bows are a little more difficult to steady on-target, since
the lighter weight doesn't feel as stable in your hand. However, since
less than 2 lbs separates the lightest and the heaviest bows on the market,
most shooters will discover that virtually any model is light enough to carry
comfortably. And even fully accessorized, most bow systems will weigh
considerably less than a typical hunting rifle. Unless you have a
specific need for a very lightweight bow, you shouldn't spend too much time
splitting hairs over whether you should get a bow that weighs 3.5 lbs or 3.8
lbs, as it is likely you'll never notice the difference. Other design
features should take much higher precedence in your selection of a new
compound bow. |
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Go Long? |
Axle-to-Axle
Length: How Short Should You Go You've probably noticed that
bows are becoming increasingly compact, with an average length just over
36". Some short axle designs are even pushing below
30". Often marketed as "more maneuverable", these stubby
designs have become quite popular, particularly for treestand hunters.
Short axle bows have a few distinct advantages beyond the obvious. Most
of the short-axle bows are quite fast, shooting at least as quickly as their
longer length counterparts. They also have noticeably less hand shock, since
most short-axle bows use a high limb deflection angle, or pre-bend. And
since their risers are generally smaller too, most shorty-bows are lighter as
well. Most importantly, you'll find that short-axle bows often have
fairly generous brace heights - allowing them to regain some of the
forgiveness lost to the short-axle design. Many shooters report that
short-axle bows shoot just as accurately as longer bows. Admittedly
this might be a stretch, but it's a close race nonetheless. Properly
tuned, short-axle bows can shoot quite well. However, most tournament
archers, who need ultimate pin-point accuracy, stick with the longer - more
stable designs. Before you choose a short-axle design, you might want
to consider a few small drawbacks though. Short-axle bows are generally
intended to be shot with a mechanical release. If you are a finger
shooter, the acute finger-pinching string angle at full-draw will make
holding back your shorty quite uncomfortable. Most finger shooters look
for bows with at least a 38-40" axle-to-axle length to avoid this
problem. You may find that not all accessories will work with the
short-axle bows either, since the risers don't offer
enough room for large sight-mounting plates and some quiver systems.
You may also have to shop around for a peep-sight that can accommodate the
acute string angle at full draw. Some standard peeps, particularly the
tube-aligned type, get over-rotated on short-axle bows and must be modified
or replaced in order to get a clear viewing angle through the hole. |
Go Short? |
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This is a hotly debated
issue in the industry. It seems that serious archers
who already have a preference for single vs. dual cams, will fight to the end
on this debate. Since the invention of the first dual-feed single-cam,
by Matt McPherson in the early 90's, virtually every bow company has
feverishly worked to develop and perfect their own single cam systems.
Though two-cam technology continues to improve, single-cam models have
continued to gain market share and are today's popular choice in the |
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