Arrow penetration is not controlled by one number. Speed, kinetic energy, momentum, arrow weight, FOC, and broadhead design all matter in different ways. None of them works alone.
The useful question is not “Does KE win or does momentum win?” The useful question is: How well does the complete arrow use its motion after impact?
Speed, mass, KE, and momentum describe the arrow before impact. Broadhead geometry, flight, alignment, structural integrity, impact angle, and the target determine how that motion is used.
What Happens Before Impact
Speed
Speed affects trajectory and how quickly the arrow reaches the target. It is part of both the KE and momentum calculations. More speed does not automatically mean more penetration.
Kinetic energy
Kinetic energy describes the energy of the moving arrow. It changes with mass and with the square of velocity:
KE (ft-lb) = arrow weight in grains × speed² ÷ 450,240
Energy is required to do work, including cutting and deforming material. The KE number still does not tell us how efficiently the broadhead uses that energy.
Momentum
Momentum is mass multiplied by velocity:
Momentum (slug-ft/s) = arrow weight in grains × speed ÷ 225,218
Momentum helps compare changes in mass and speed. It is not force, inertia, energy retention, or a penetration score.
What Controls Penetration After Impact
| Factor | Why it matters |
|---|---|
| Broadhead sharpness | A sharp edge requires less work to begin and continue a cut. |
| Broadhead profile and mechanical advantage | Blade angle, width, and cutting diameter change resistance. |
| Arrow flight | An arrow arriving out of line can waste motion and increase resistance. |
| Alignment | A broadhead, insert, and shaft that do not run true can work against each other. |
| Structural integrity | Bent, broken, or separated components stop functioning as one system. |
| Impact angle | The arrow may face more resistance at an angle than on a straight impact. |
| Target medium | Gel, foam, hide, tissue, and bone do not resist an arrow the same way. |
Why Test Results Can Disagree
A test can only answer the question it was designed to test. Change the broadhead, target, speed, angle, or arrow structure and the result can change.
In a controlled ballistic-gelatin study using projectiles of identical shape, kinetic energy correlated more strongly with penetration than momentum or speed. That finding applies to that test. It does not mean KE alone predicts every hunting impact.
The Ashby field reports observed complete arrow and broadhead systems under real impact conditions. Those reports are valuable because they examine factors such as structure, sharp fixed heads, FOC, and heavy-bone contact. They also come from specific equipment, animals, angles, and field methods.
Both types of evidence are useful when they are kept in context. Neither supports a universal promise that one momentum number, one KE number, or one finished weight guarantees a pass-through.
Where Arrow Weight Fits
From the same bow, a heavier arrow normally leaves slower and often carries more momentum. A lighter arrow normally leaves faster and has a flatter path. KE may stay close across a practical range.
That is why the Everyday Arrow Weight Formula does not chase maximum mass. It looks for a bow-specific target that balances useful trajectory with arrow mass and performance.
Where FOC Fits
FOC describes where the arrow balances compared with its midpoint. It affects weight distribution and flight behavior. Standard industry guidance is commonly 10–15 percent. My working guidance is 13–18 percent for hunting arrows, with more than 20 percent considered high FOC.
FOC is not a penetration guarantee. More front weight also changes finished weight and usually weakens dynamic spine. Plan it before the final build and verify it after the test arrow is complete.
Where Broadhead Design Fits
Broadhead sharpness, blade angle, cutting diameter, strength, and alignment can change how much resistance the arrow faces. A fixed head is not automatically more accurate, and a mechanical head is not automatically less effective. The complete design has to match the arrow, bow, and tune.
A fixed blade has more steering surface and can make a tune or alignment problem easier to see. A mechanical design must deploy and may have a larger cutting diameter. Those are design tradeoffs, not universal winners.
Perfect Flight Comes First
An arrow that is not leaving the bow cleanly starts the penetration problem before it reaches the target. Start with the manufacturer’s spine chart, check the planned setup with the Dynamic Spine Calculator, and then verify the real arrow through paper tuning, walk-back or group tuning, and broadhead testing.
A Better Way to Think About Penetration
- Use the Formula to set a practical finished-weight range.
- Compare speed, KE, momentum, and trajectory without turning one into a pass/fail score.
- Plan total component weight and FOC together.
- Check static and dynamic spine.
- Use a sharp, aligned, structurally sound broadhead system.
- Build one test arrow and prove its flight before the batch.
The Bottom Line
Penetration is a system outcome. A well-built arrow gives the bowhunter control over the factors that can be controlled: weight, speed range, FOC, spine, broadhead design, alignment, structure, and flight. The Everyday Arrow System is designed to solve those decisions in the right order.
Your Next Steps
Use the Everyday Arrow System in this order:
- Set the finished-arrow target.
- Compare speed, KE, and momentum.
- Plan and measure FOC.
- Check the proposed shaft.
- Build and verify the complete arrow.
Build one test arrow before you commit to a full batch. That is where the numbers become a real setup.
Want to see exactly what I’m carrying this season? Check out my Personal Bowhunting Gear List for 2026
