4mm Arrows Guide: Benefits, Trade-Offs & Who Should Shoot Them

4mm Arrows: The Quick Answer

A 4mm arrow makes the most sense when you specifically want the advantages of a smaller-diameter shaft.

For me, the biggest advantage is what happens as distance and wind increase. There's simply less shaft surface exposed to a crosswind than there is with a larger-diameter arrow.

The smaller shaft also means less shaft surface has to move through the target after the broadhead has created the wound channel.

Those advantages are real, but they don't automatically make a 4mm arrow faster, heavier, more durable or better tuned.

What Is a 4mm Arrow?

A 4mm arrow is a micro-diameter shaft that is smaller than the more common 5mm and 6.5mm hunting-arrow classes.

You'll also hear a lot of 4mm shafts referred to as .166-class arrows because of their approximate inside diameter.

The important thing isn't really the name. It's the fact that the shaft itself presents less surface area to the air and less shaft diameter behind the broadhead.

Where people get this wrong is assuming shaft diameter tells you everything about the finished arrow.

It doesn't.

You can build a relatively light 4mm arrow or a fairly heavy one. GPI, shaft length, spine and components determine finished weight — not diameter by itself.

The same is true with durability. A smaller shaft isn't automatically stronger or weaker just because it's 4mm. Carbon construction, wall thickness and the front-end component system all matter.

The Biggest 4mm Advantage: Less Shaft in the Wind

This is the biggest reason I would personally consider moving somebody into a 4mm arrow.

The smaller the shaft diameter, the less surface area you're putting sideways into a crosswind.

That doesn't make a 4mm arrow immune to wind. Vanes, arrow speed, total weight, distance and the actual wind conditions still matter.

But all else being equal, a smaller-diameter shaft gives the wind less arrow to push against.

At 20 or 30 yards in the whitetail woods, that advantage may not matter enough for you to care.

At 60, 80 or 100 yards on a TAC course, or hunting out West where you're dealing with more distance and open-country wind, it starts becoming a lot more relevant.

Do 4mm Arrows Penetrate Better?

Potentially, but this is where I think the marketing gets ahead of the actual explanation.

Once the broadhead enters the animal, the shaft still has to follow it through the wound channel.

A 4mm shaft has less exterior surface area than a larger-diameter shaft, so there can be less shaft contact and friction as it continues through the target.

That's a legitimate advantage.

But I would not tell somebody that moving from a 5mm arrow to a 4mm arrow automatically guarantees a pass-through or suddenly fixes a penetration problem.

The broadhead, total arrow mass, momentum, impact angle, shot placement and tune are all part of the system.

A properly built and tuned 5mm arrow is going to outperform a poorly built 4mm arrow every time.

Do 4mm Arrows Shoot Faster or Flatter?

Not automatically.

This is another place where diameter and weight get mixed together.

Initial arrow speed is driven primarily by the bow and the finished mass of the arrow.

If your 4mm arrow finishes lighter than your 5mm arrow, then yes, it's probably going to leave the bow faster.

But that's because it's lighter, not because the shaft is 4mm.

The smaller diameter can reduce aerodynamic drag as the arrow travels downrange, which becomes more meaningful over longer distances, but I wouldn't build a hunting arrow around diameter alone just to chase trajectory.

If flatter trajectory is the goal, you still have to look at total finished weight, spine and the rest of the setup.

4mm Components: Where the Build Gets More Complicated

This is probably the biggest downside of going to a 4mm shaft.

There just isn't as much room inside the shaft for a traditional component system, so manufacturers have to solve the front end differently.

Depending on the arrow, you may be using an outsert, half-out or another external component system to get back to a standard 8-32 broadhead thread.

That's not necessarily bad, but now the quality and alignment of that component matter a lot.

If the front-end component isn't square or aligned properly, broadhead flight can suffer.

It's also another place where finished weight can change quickly. A shaft may look light on paper, but once you add a heavier stainless or titanium front component, the complete arrow may end up much heavier than you expected.

That's why you've got to look at the complete system instead of choosing an arrow based only on shaft GPI.

And just like any other arrow build, adding more weight to the front dynamically weakens the shaft. Make sure spine is still appropriate for your draw length, draw weight, shaft length and point weight.

If you're unsure how those variables work together, read our guide to choosing the right arrow for your bow.

Are 4mm Arrows Less Durable?

Not just because they're 4mm.

Durability depends on the actual shaft construction, wall thickness and component system.

What we do pay extra attention to on 4mm builds is the front end.

A lot of these arrows rely on an outsert or half-out that extends outside the shaft. That component is taking a lot of leverage when the arrow hits at an angle or impacts something hard.

We've seen aluminum components bend. Stainless and titanium systems can increase strength, but they also add weight and cost.

That's the trade-off.

When I'm looking at a 4mm hunting arrow, I'm evaluating the shaft and the component system together. I don't really care how good the shaft is if the front end isn't something I trust.

4mm vs 5mm: Which One Would I Choose?

For most bowhunters, I still think 5mm is the all-around sweet spot.

You get a relatively small shaft, a huge range of proven component systems, a lot of shaft choices, and it's generally easier to build and maintain.

That's why I use 5mm for a lot of my own hunting and hybrid hunting/TAC setups.

I would move to 4mm when the smaller diameter becomes valuable enough to justify the more specialized front end.

If I'm spending a lot of time shooting distance, dealing with open-country wind, or building specifically around a micro-diameter platform, 4mm starts making a lot more sense.

If you want a full breakdown of all three common hunting-arrow sizes, read our 4mm vs 5mm vs 6.5mm arrow guide.

Who Should Shoot 4mm Arrows?

If somebody comes into the shop and tells me they hunt mostly from a tree stand and their shots are 20 to 30 yards, I'm probably not telling them they need a 4mm arrow.

They can absolutely shoot one, but the advantages probably aren't changing much about that application.

If that same person tells me they're shooting TAC, hunting elk in open country, practicing at 80 or 100 yards, or dealing with wind on a regular basis, now we have a reason to talk about 4mm.

That's how I would make the decision.

Don't start with, "What's the smallest arrow I can shoot?"

Start with, "What am I trying to make this arrow do?"

4mm Arrow Platforms We Like

Two of the 4mm platforms we work with regularly at Extreme Outfitters are the Easton Axis 4mm and Victory VAP TKO.

If you're considering the Axis specifically, our Easton Axis Arrows Guide goes deeper into the differences between Axis 4mm and 5mm.

Bottom Line

4mm arrows aren't automatically better hunting arrows.

They're a more specialized tool.

The smaller diameter gives you less shaft exposed to crosswind and less shaft surface following the broadhead through the target. Those advantages become more meaningful as distance and wind increase.

What you give up is some simplicity.

Component systems become more important, builds can cost more, and you need to pay attention to front-end alignment and finished weight.

For somebody shooting normal whitetail distances, I'd have no problem staying with a good 5mm or even 6.5mm shaft.

For somebody shooting distance, hunting open country or specifically trying to reduce the arrow's profile in the wind, 4mm can absolutely make sense.

Like everything else with arrows, don't chase one feature. Get the spine right, build the complete system correctly, and choose the diameter that actually fits what you're trying to do.