Arrow setup for a compound bow

An arrow is six parts: shaft, point (or broadhead), insert, nock, fletching, and the glue and wraps that hold it all together. Every spec choice you make picks tradeoffs across these — pick a heavier point, dynamic spine softens; pick a longer shaft, dynamic spine softens further and trajectory drops faster; add weight forward, FOC rises, momentum rises, drop increases.

Shaft

The tube. Three numbers describe it: spine (stiffness — lower number means stiffer in the AMO/ATA system), GPI (grains per inch — raw mass density of the bare shaft, typically 7.5–11 for hunting), and length (measured from the throat of the nock to the end of the shaft, before insert and point).

Point or broadhead

The business end. Comes in standard weights — 75, 85, 100, 125, 150, 175, 200+ grains. Field points are essentially uniform mass forward; broadheads add steering surface and amplify any setup error. Heavier point means more FOC and weaker dynamic spine.

Insert

The threaded sleeve bonded into the front of the shaft that the point screws into. Standard aluminum inserts run roughly 12–16 grains. Brass FOC-heavy inserts can run 50–100 grains and are how the heavy-arrow camp loads weight forward without going to a 200-grain point. Outserts (collars that fit over the outside of the shaft) appear on micro-diameter shafts like the Easton 4mm series.

Nock and fletching

Nock weight is small (around 8–10 grains for a standard pin nock; 16–25 for a lighted nock). Fletching is plastic vanes or feathers — typical hunting setups use three 2–3" vanes weighing 5–10 grains each. Helical or offset orientation imparts spin, which stabilizes broadheads. More vane surface steers better; less vane gives slightly higher FOC.

Spine is the stiffness of the shaft. The published number is the static spine: how far an unfletched shaft deflects under a standardized weight (per the AMO/ATA test, an 880-gram weight hung at the center of a 28" supported span). Lower number means stiffer. A 300-spine shaft is stiffer than a 400-spine shaft.

What you actually care about when tuning is dynamic spine — how the shaft flexes when launched. Dynamic spine depends on static spine plus point weight (heavier softens), arrow length (longer softens), bow draw weight (more force softens), cam aggressiveness, and release type. Static spine is a property of the shaft. Dynamic spine is what your bow sees.

Use the chart

Don't eyeball spine. Open the manufacturer chart for the shaft you're considering — Easton, Gold Tip, Black Eagle, Victory all publish them as PDFs. Cross-reference draw weight × finished arrow length × point weight. The chart returns a spine bucket (commonly 250, 300, 340, 400, 500). Most modern 60–70 lb compound hunters with a 28–30" draw and a 100-grain point land around 340 spine, but the chart is authoritative — buckets shift with draw length and point weight, and the bands aren't identical across manufacturers.

Over and underspined

Arrows that are too weak (underspined) for your setup typically produce a tail-left paper tear for a right-handed shooter — the shaft flexes too much during launch and exits nock-left. Tail-right is the stiff (overspined) signature. Vertical tears are almost always nock-point or rest-height issues, not spine.

Spine tears can resist rest tuning. If you've moved windage as far as it will go without fixing the tear, the problem isn't centershot — it's spine, cam lean, or contact. Stop chasing the rest.

The single most-argued question in modern bowhunting. Both schools shoot dead deer; the honest answer depends on what you're hunting and how far.

Light (350–400 gr)

Faster, flatter trajectory, more kinetic energy at the muzzle, less margin against wind drift downrange. Stresses the bow more (less mass to absorb the limbs' stored energy means more vibration and noise). Below 5 grains per pound of peak draw weight is unsafe per every major bow warranty.

Mid (400–500 gr)

The historical North American whitetail standard. Best balance of speed and momentum. Most hunters end up here without thinking about it.

Heavy (500–650 gr)

Slower, more momentum, deeper penetration on game, less wind-affected once flying, quieter bow at the shot. More drop at distance, which raises the cost of a range-estimation error. The Ranch Fairy / John Dudley camp favors this band for larger North American game.

Very heavy (650+ gr)

Ashby-thesis territory. Targeted at very large or thick-skinned game (cape buffalo, moose, brown bear). Outside that context it's overkill, with significant trajectory cost.

The two schools

The heavy-arrow / high-FOC argument leans on Dr. Ed Ashby's penetration studies and is championed today by John Dudley, Ranch Fairy, and the Ashby Bowhunting Foundation's "Top 12 Penetration Factors." The thesis: penetration on big game correlates with momentum, structural integrity, and forward weight bias far more than it correlates with kinetic energy. This argument grows stronger as game size and bone risk grow.

The flat-trajectory school — historically promoted by speed-bow marketing through the 2000s, and supported by plenty of veteran whitetail hunters — argues that modern compound bows have plenty of energy to kill whitetail-class game cleanly with mid-weight arrows, and that flat trajectory reduces range-estimation error, which is the dominant cause of bad shots in the field.

Honest summary: at whitetail-class game and reasonable shot distances, both setups work. The heavy-arrow argument's leverage compounds (pun intended) on elk, moose, and larger.

FOC is the percentage of your arrow's length by which its balance point sits forward of physical center. A 30" arrow that balances at 16.5" from the nock has its balance point 1.5" forward of center, which is 5% of arrow length — so 5% FOC.

FOC% = ((balance_point − arrow_length / 2) / arrow_length) × 100

Typical bands across published sources:

• Target / 3D / indoor: 7–11%
• General hunting: 10–15% — most modern setups land here
• EFOC (extreme FOC, Ashby term): 19–25%
• Ultra-EFOC: 30%+ — rarely seen outside dangerous-game setups

What FOC actually does

Higher FOC means the arrow recovers from launch flex faster (cleaner downrange flight, especially with broadheads) and concentrates more mass forward of impact (deeper penetration on game). The cost is trajectory: front-loaded arrows nose down sooner, so long-range groups can suffer above ~25% FOC. Above ~20%, vanes have less leverage to steer the heavier front, and broadhead steering can degrade.

How to add FOC

In rough order of effect: heavier point (100 → 125 → 150 → 175 grains), heavier insert (aluminum 16 gr → brass 50–100 gr), smaller or lighter vanes, lighter nock. Adding point weight is the strongest lever, but it also softens dynamic spine, so chasing FOC often forces a re-spine of the shaft. The interactive lab makes this trade visible — bump the point weight and watch the recommended spine shift.

How much FOC is enough — the actual debate

Where the curve flattens is contested, and worth being upfront about. The Ashby Bowhunting Foundation position is that there's effectively no upper limit for hunting performance — their published "Top 12 Penetration Factors" pushes setups into the 19–25% band and beyond, arguing that more forward weight produces better bone-breaking outcomes on big game with no meaningful cost.

Practical archery instructors and target shooters tend to call diminishing returns earlier — somewhere around 12–18% — pointing to degraded broadhead steering, slower vane recovery, and worsening trajectory at the long end of typical ranges. Lancaster Archery's tuning content sits in this camp, as do most target-3D coaches.

Both sides agree on one thing: setups under about 8–10% FOC steer broadheads worse and penetrate worse than setups in the 12%+ range. The disagreement is where above 12% the curve flattens — and how much trajectory you're willing to give up for more forward weight. For whitetail-class hunting at typical bowhunting distances, the difference between 13% and 18% FOC is small in the field. For elk, moose, or larger, the heavier-FOC argument's leverage grows.

The two ways to talk about how hard an arrow hits — and they don't say the same thing.

KE (ft-lb) = (grains × fps²) / 450,240
Momentum (slug-fps) = (grains × fps) / 225,218

Kinetic energy scales with velocity squared. Momentum scales with velocity linearly. So a light, fast arrow looks better on a KE chart than a heavy, slow arrow of the same kinetic energy — but the heavy arrow has more momentum.

Why the distinction matters for hunters: penetration on game correlates more closely with momentum, sectional density, and broadhead profile than with kinetic energy alone. This is the physics core of the Ashby argument, and it's why two arrows that "produce the same energy" can perform very differently on a tough shot.

Commonly cited KE thresholds

These appear in Easton's hunting bow setup material and most state hunter-education curricula. They're guidance, not regulation.

• Small game / turkey: 25 ft-lb minimum
• Whitetail / antelope / mule deer: 40 ft-lb
• Elk / black bear / wild boar: 50 ft-lb
• Moose / large African plains game: 65 ft-lb
• Cape buffalo and dangerous African: 80–100 ft-lb

Almost any modern 60+ lb compound setup with a hunting-weight arrow clears the whitetail and elk numbers comfortably. Once you're in that range, momentum and broadhead choice do more for clean kills than chasing a higher KE number.

The fps printed on a bow's spec sheet is a marketing number measured under the industry's standardized test conditions — not the speed your bow actually shoots.

IBO speed is measured with a 350-grain arrow (5 grains per pound at 70 lb peak), 30" draw length, 70 lb peak draw, mechanical release, and no string accessories. ATA speed is similar but slightly more conservative, allowing minimal accessories. ATA tends to come in roughly 5–8 fps below IBO for the same bow.

Real-world fps drops from those numbers as soon as your setup deviates. Approximate rules of thumb (cross-check with your bow manufacturer's published loss tables):

• About 10 fps lost per inch of draw length below 30"
• About 2 fps lost per pound of peak draw below 70 lb
• About 1 fps lost per ~3 grains of arrow weight added beyond 5 gpp
• A few fps lost for each string accessory (peep, kisser, silencer)

A typical 70 lb / 28" draw / 450-grain hunting setup chronos roughly 40–60 fps slower than the bow's IBO rating. That's normal. If you want exact fps, use a chronograph; everything else is an estimate.

Field points have minimal aerodynamic surface ahead of the shaft. Launch errors — cam lean, weak or stiff spine, fletching contact, rest centerline drift — don't affect them much. They're forgiving.

Broadhead blades act as forward steering surfaces. They amplify any setup imperfection. A clean field-point group at 30 yards with broadheads drifting four to eight inches off the same point of aim is almost always a tuning issue, not a defect in the broadhead. Standard fix sequence:

1. Paper tune to a clean tear (or close to it).
2. Walkback or French tune to confirm rest centerline.
3. Bareshaft tune at 15–30 yards (bareshaft impacts within 1–2" of fletched).
4. Broadhead tune: micro-adjust the rest until broadheads hit the field-point group.

The paper tuning guide covers steps one and two in detail.

Fixed-blade vs mechanical

Fixed-blade heads (Iron Will, Magnus, G5 Montec, Slick Trick) are proven on penetration and have no moving parts to fail. They demand a tuned bow. Heavier blade material penetrates better but raises tuning sensitivity.

Mechanical / expandable heads (Rage, Sevr, Grim Reaper) fold during flight, deploy on impact. More forgiving in the air, larger wound channel, but they use some of the arrow's energy on deployment and historically lag fixed blades on heavy bone. Modern hybrid mechanicals have closed much of that gap.

The heavy-arrow / Ashby camp strongly favors single-bevel fixed-blade heads — the rotational moment on impact helps split bone rather than glance off it.

If you'd rather skip the chart math and get going, these are reasonable defaults for three common hunting profiles. Adjust based on your own bow, draw length, and the spine chart for the shaft you choose.

What spine do I need?

Read it off a manufacturer chart (Easton, Gold Tip, Black Eagle, Victory all publish them). Cross-reference your peak draw weight, your finished arrow length, and your point weight. Most 60–70 lb compound hunters with a 28–30" draw and a 100-grain point land somewhere around 340 spine, but use the chart — heavier points and longer arrows shift you weaker (higher number); shorter arrows shift stiffer (lower number).

Good arrow weight for whitetail?

425–475 grains is the modern norm for whitetail-class hunting and works well at typical bowhunting ranges. 400 grains is fine. 500+ adds penetration margin with little real downside on whitetail-distance shots under 40 yards. The 5-grains-per-pound floor (so 350 gr at 70 lb) is the manufacturer minimum for safety, not a hunting recommendation.

Is high-FOC actually better?

For penetration on big game, yes — within reason. Higher FOC concentrates mass forward, improves recovery from launch flex, and steers broadheads more cleanly. Diminishing returns kick in around 20%. For target and 3D, modest FOC (around 10–13%) flies flatter at distance. For whitetail-distance shots, the difference between 12% and 18% FOC is small in practice.

Why don't my broadheads group with my field points?

Almost always a bow-tune issue, not a broadhead defect. Broadhead blades amplify any setup imperfection — cam lean, weak or stiff spine, fletching contact, or rest centerline error. The fix sequence is paper tune → bareshaft tune → broadhead tune. Don't blame the broadhead until you've bareshaft-tuned.

How much kinetic energy do I need for whitetail or elk?

Commonly published guidance puts whitetail-class game at 40 ft-lb minimum, elk and black bear around 50, moose and very large game 65 or more. These thresholds appear in Easton's hunting setup material and most state hunter-education curricula but aren't legally binding. Almost any modern 60+ lb compound setup clears the whitetail and elk numbers comfortably; momentum and broadhead choice matter more once you're in that range.

100, 125, or 150 grain points?

100 if your spine chart points there and you don't want to re-tune. 125 is the strong default for modern hunting setups — better FOC and momentum, broadhead selection is still excellent, modest spine impact. 150+ for heavy-arrow builds; expect to drop a spine class to keep the dynamic spine in range.

How does arrow length affect spine?

Longer arrows are weaker in dynamic spine, shorter are stiffer. Cutting an inch off a shaft is enough to shift it noticeably toward stiff. This is why every spine chart has both a draw-weight axis and a length axis. Cut to your draw length plus 0.5–1" of overhang past the rest for safe clearance.

Heavy arrow or fast arrow — which is better for hunting?

Fast arrows forgive range-estimation errors (flatter trajectory). Heavy arrows forgive shot-placement errors on bone or large game (more momentum, deeper penetration). For most North American hunting under 40 yards, a balanced mid-weight setup around 450–500 grains wins. The heavy-arrow argument grows stronger as game size and bone risk increase.

What's the minimum arrow weight my bow can safely shoot?

5 grains per pound of peak draw weight is the universal manufacturer floor. So a 70-lb bow needs a 350-grain minimum. Below that voids your warranty and stresses the bow toward dry-fire territory — there isn't enough mass to absorb the stored energy of the limbs.

Do I need to re-tune if I change point weight?

For any swing larger than about 25 grains, yes. Going 100 → 125 grain softens dynamic spine; you may need a stiffer shaft, a small rest adjustment, or both. Re-paper-tune and re-broadhead-tune after any point-weight change.

Spine

Static stiffness of the arrow shaft, expressed as deflection × 1000 under the AMO/ATA test. Lower number means stiffer.

Dynamic spine

How the shaft actually flexes when launched. Affected by point weight, arrow length, draw weight, cam type, and release.

GPI

Grains per inch — mass of the bare shaft per inch of length. Multiply by length to get bare-shaft weight.

FOC

Front of Center. Percentage of arrow length the balance point sits forward of physical center. Typical hunting: 12–15%.

KE

Kinetic energy of the moving arrow in foot-pounds. KE = (grains × fps²) / 450,240.

Momentum

Mass × velocity, in slug-feet-per-second. M = (grains × fps) / 225,218. Better predictor of penetration than KE alone.

IBO speed

Bow speed measured per IBO standard: 350-gr arrow, 70 lb, 30" draw, no string accessories.

ATA speed

Bow speed measured per ATA standard. Slightly more conservative than IBO, with limited accessories permitted.

gpp

Grains per pound — total arrow weight divided by bow peak draw weight. 5 gpp is the universal manufacturer minimum for safety.

Insert

Threaded sleeve bonded inside the front of the shaft to receive points and broadheads.

Outsert

Collar that fits over the outside of the shaft. Common on micro-diameter shafts like the Easton 4mm series.

Broadhead

Bladed hunting point. Fixed-blade or mechanical (expandable).