The Easton spine chart is the first thing every new archer Googles. It's also the most misunderstood document in the sport. The chart gives you a ballpark. Your actual setup decides what you shoot.
Spine isn't static. Dynamic spine — what the arrow does when it actually fires — depends on point weight, arrow length, cam aggression, release type. Two archers at 70 pounds and 29 inches can need different spines.
The Chart Cheat Sheet
Standard Easton starting point for a 28" arrow with a 100 grain point on a modern compound:
- 40-50 lb draw weight: 500 spine
- 50-60 lb: 400 spine
- 60-70 lb: 340 spine
- 70-80 lb: 300 spine
- 80+ lb or heavy point: 250 spine
That's the start. Now adjust.
The Adjustments That Matter
Go stiffer (lower spine number) when:
- Arrow is longer than 28". Every inch over 28 = roughly one spine class stiffer.
- Point weight is over 100 grains. A 125 grain point = about half a class stiffer. A 150 grain point = a full class.
- You shoot a high-let-off, aggressive cam (more on that below).
- You shoot a hard-punch release (thumb vs back tension).
Go weaker when:
- Arrow is shorter than 28".
- Point weight is under 100 grains.
- You shoot a smoother cam.
Which Cams Are Actually Aggressive
Most posts get this wrong. The Hoyt RX-9 and RX-10 are not aggressive cams. They're actually examples of smooth cams — drawn-out wall, forgiving back end. Mathews Phase 4 is also on the smoother side.
Real aggressive cams that punish a weak spine:
- PSE Sicario: Crazy fast. Aggressive draw cycle. Allows for 70% let-off which helps a ton at the back wall, but the cam is unforgiving on dynamic spine. Build stiff.
- PSE Omen: Historically known as a speed bow. Aggressive cam. If you're running an Omen and a 340 with a 125 grain point, you might find yourself a class light.
If you shoot a smooth cam (RX-9, RX-10, Phase 4) you get more forgiveness with a weaker spine. Aggressive cam, build stiffer than the chart says.
Let-Off — My Rule
Elite has been known for years for offering up to 90% let-off on bows like the Ethos and Exalt-35. Other brands have caught up — PSE Mach 33 DS goes to 90% too. Hoyt and Mathews flagships top out around 85%.
I would never recommend let-off that high. I don't want anyone going above 80%.
My sweet spot tends to be 70-75% — whatever gets me between 20-21 pounds holding weight.
Here's why I think 90% is a trap. Less holding weight means less back tension. With high let-off, hand torque, face pressure, and grip slop have a disproportionate effect on pin float and shot execution. Target shooters universally run 65-75% for accuracy. Hunters lean higher for the sit-and-wait. There's a middle ground — and 90% is past it.
The forum way of saying it: "more let-off, more slop." That matches what I see on the line.
Why Dynamic Spine Beats the Chart
Two 340 spine arrows from different brands don't shoot the same. An Easton FMJ 340 is built different from a Black Eagle Spartan 340. Wall thickness, carbon weave, straightness tolerance — all of it changes how the arrow flexes around the riser.
This is why bareshaft tuning exists. Build the arrow per the chart, shoot it with fletchings removed at 20 yards, watch where it lands relative to a fletched arrow. Bareshaft left of fletched (RH shooter) = arrow reading weak. Right = stiff.
Chart gets you 80% there. Bareshafts get you the rest.
Heavy-Point Reality
The trend toward 175 and 200 grain points has broken the chart for half the hunting world. A 70 lb shooter with a 29" draw running a 200 grain head up front needs a 250 spine, not a 340. See the arrow weakening post for the math. Every 25 grains up front is equivalent to about an inch of arrow length added.
Most archers don't adjust. They shoot a chart-correct 340 with 175 up front and wonder why their broadheads tail left at 40 yards. Spine reads weak because dynamic spine collapsed.
The Brands and What They Actually Are
- Easton FMJ: Heavy, durable, slightly weaker dynamic spine than printed. Add a spine class for safety.
- Easton Axis 5mm: The reference standard. Numbers match real world.
- Easton Match Grade (Axis or FMJ): Tighter spine tolerance, +/- 0.0015" straightness. Numbers match.
- Gold Tip Pierce Platinum: Slightly stiff for the printed spine. A 340 reads like a 325.
- Black Eagle Spartan: Reads weak. 340 acts like 360 in dynamic flex.
- Victory VAP TKO: Small diameter, premium tolerance. Numbers match.
How to Actually Decide
Start with the Easton chart. Adjust for point weight, length, cam, and let-off. Pick a brand based on what you can afford and how durable you need it. Build three or four arrows. Bareshaft tune at 20 yards. The result tells you if you got the spine right.
The Forge handles this whole calculation. Enter draw weight, draw length, arrow length, point weight, insert weight, and shaft brand. It returns a recommended spine with the dynamic adjustments baked in. It also flags when you're at the edge of two classes and should test both.
The Honest Answer
If you're 60-70 lb at 28-29" draw shooting 100-125 grain points, get a 340. Heavy up front (150+)? Get a 300 or 250. Aggressive cam like a Sicario or Omen? Build stiff. Bareshaft tune to confirm. Don't overthink it.