Part 1: Momentum Explained: How Arrow Weight Impacts Penetration (More Than You Think)

“Your bow doesn’t kill the deer — the arrow does.”

It’s something I say often, and for good reason.

A fast bow doesn’t mean much if your arrow doesn’t do its job after the shot. That’s why momentum, not just speed or kinetic energy, is the foundation of real-world penetration.

As a retired U.S. Army Green Beret, I’ve spent my life relying on momentum — literally. Whether it was breaching doors or launching heavy equipment downrange, I learned that mass in motion does the damage. The same principle applies to arrows. A fast bow doesn’t kill the deer. A properly built arrow does. And if you don’t understand how momentum works, your arrow might hit — but not penetrate.

In this post, we’re going to walk through:

• What momentum is (in plain terms)
• How it compares to kinetic energy
• What arrow weight has to do with it
• Why momentum is driven by inertia, not just impact force
• What this means for arrow builds that actually work on game animals

Let’s break it down.

This is Part 1 of The Performance-Driven Arrow Build Series ➜

🔗 Next up: Part 2 – How to Choose the Right Arrow Weight ➜

What Is Momentum?

Momentum is the arrow’s ability to keep moving forward after impact.

The higher your momentum, the harder it is for something (like bone or muscle) to stop your arrow. It’s a simple physics formula:

Momentum = (Arrow Weight × Speed) / 225,218

It’s measured in slug feet per second (slug·fps), which may not mean much to most hunters. But the takeaway is this:

Momentum shows how much inertia your arrow carries. And inertia is the real killer. It’s what drives the arrow through the deer, not just into it.

Learn more about the Physics of Arrow Penetration here.

Momentum vs. Kinetic Energy

Kinetic Energy (KE) is how much energy your arrow has at the point of release.

Momentum is how much it can maintain direction and force after hitting resistance.

• KE = how hard the arrow hits
• Momentum = how well it keeps going

Think of it like this:

• A lightweight arrow can hit hard, but it’s easier to stop.
• A heavy arrow may start slower, but it plows through with more force.

Momentum is a better predictor of penetration, especially on shoulder shots, steep angles, or larger animals.

Why Inertia Is the Real Force Behind Lethal Arrows

You can have all the bow speed in the world, but that energy needs to be carried by something, and that something is mass.

That’s inertia — the tendency of an object in motion to stay in motion.

A heavier arrow resists deceleration. It’s harder to stop. And when it hits something solid (like a rib, scapula, or thick hide), inertia keeps it moving forward.

That’s why I often say:

“The bow launches the arrow, but the arrow does the killing.”

If your arrow can’t punch through, you risk:

• Poor penetration
• Bad blood trails
• Non-lethal hits

That’s not acceptable. Not if we care about clean, ethical harvests.

Real-World Momentum Benchmarks

According to testing and field data:

• 0.30–0.35 slug·fps is good for small to medium game (like whitetails).
• 0.40+ slug·fps is ideal for tough angles or bigger animals.
• 0.50+ slug·fps is excellent for deep penetration and pass-throughs.

Now, that doesn’t mean you need to chase the heaviest arrow possible. But it does mean you should build your arrow for the job, with a real momentum target in mind.

Want to know your momentum?

🔗 Use the Arrow Speed, Kinetic Energy, and Momentum Calculator to enter your draw weight, draw length, arrow weight, and see your actual momentum value.

Example Comparison

Same bow, different arrows. The 525-grain arrow only loses 30 fps but gains significantly in momentum. That’s real-world penetration power.

The Bottom Line

Speed helps with trajectory. But inertia — and the momentum it creates – is what gives your arrow the power to punch through ribs, muscle, and bone.

If you want to build lethal arrows:

1. Focus on total arrow weight.
2. Optimize your setup for momentum.
3. Don’t chase speed at the cost of penetration.

Momentum is the invisible force behind clean kills — and now you know why.

🔗 Next up: Part 2 – How to Choose the Right Arrow Weight ➜

Or jump to Part 3 – Best Arrow Weight for Hunting ➜

Or see the full Performance-Driven Arrow Build Series ➜

Let’s build arrows that do more than hit. Let’s build arrows that kill.