Arrow Spine Comparison: 300 vs 340 vs 350 vs 400 vs 500

100 points of deflection: a 300 shaft bends 0.300 inches under the 1.94 lb / 26-inch test, a 400 bends 0.400 inches — the 300 is about one full grade stiffer and typically 8–12% heavier per inch (GPI) in the same shaft family. On a bow, that stiffness difference is worth roughly 8–10 lb of draw weight: a 70 lb / 30″ draw needs the 300, a 62 lb / 29″ draw needs the 400. Between them sits 340 (or the Victory-style 350). If your setup lands inside 2 lb of the crossover — 65–68 lb at 29″ — buy one test shaft of each and let the paper tune decide, because cam aggressiveness shifts the boundary more than the chart can show.

For a 70 lb compound, the decision tree lands 340 as the default: 29″ draw with a 100 gr point shoots 340 in roughly three of four 70-lb setups. Choose 300 instead when any of these are true: your draw is 30″ or longer, you shoot a 125–150 gr broadhead, your bow has an aggressive hard cam, or you're building a high-FOC arrow with 175+ grains up front. Choose 340 and verify with paper: a bullet hole confirms it, a tail-right tear (right-handed shooter) means you under-spined and need the 300.

The crossover sits at about 62–63 lb of draw weight at a 29-inch draw with a 100-grain point. Under that, take 400; over it, take 340. Three corrections move the line: a 30″ draw pushes a 63 lb bow toward 340; a 28″ draw lets a 65 lb bow stay on 400; a 150 gr head pushes everything one grade stiffer (so a 58 lb bow can need 340). Finger-release shooters add one more wrinkle — a mechanical release loads the shaft harder than fingers, so recurve and traditional shooters can usually run one grade weaker than the same-poundage compound. When in doubt at the boundary, paper-tune one of each: the arrow that tears a clean bullet hole is your grade, and the other is a paperweight or a lighter-bow arrow.

About one full grade in flex — but with a brand-labeling trap. Easton-style numbering runs …340, 400…, while Victory and some Carbon Express lines use 350 as their hunting grade, and a measured '350' often deflects 0.340–0.350″, making it nearly identical to an Easton 340. So '350 or 400' is really 'the 60–65 lb hunting grade or the 55–58 lb grade.' Use 350 for 58–64 lb compounds with 100–125 gr heads and 30″ draws; use 400 for 55–58 lb, shorter draws, or lighter 90–100 gr points. Never compare a 350 label to a 340 label across brands without a deflection check — measure both at 26″ with a 1.94 lb load (see the spine tester page) and match numbers, not labels.

The weaker (higher-number) shaft is almost always the more forgiving choice: 400 bends more around the riser, clears the rest with less clearance demand, and tolerates form inconsistencies better than an over-stiff 340. A slightly too-weak arrow also warns you honestly — tail-right paper tears and broadhead tears that correct with a lighter point — while a too-stiff arrow often hides its symptom until broadheads expose it. The exceptions: heavy 125–150 gr points weaken dynamic spine (so the 'forgiving' 400 can become genuinely under-spined), and aggressive hard cams punish weak spine harder than smooth cams. So default to the weaker grade only when your point weight is 100–125 gr and your cam is moderate.

They're intermediate grades on the same scale — a 320 deflects 0.320″ (a bit stiffer than 340, a bit weaker than 300) and a 330 sits just under 340. A handful of shaft makers — mostly micro-diameter and European/Asian target lines — cut grades between the Easton-standard 250/300/340/400 ladder to offer finer tuning steps, the way rifle handloaders get between standard powders. They behave as expected on the deflection scale: buy 320 when a 340 paper-tunes tail-right but you don't want the full jump to 300, and 330 when 340 is just barely too weak. Two cautions: fewer fletching/nock accessories are stocked for odd grades, and resale value is lower — for hunting, the standard grades at ±½ point-weight adjustment usually make more sense.

450 is the intermediate grade between 400 and 500: it deflects 0.450″, roughly half a grade weaker than 400. It's the answer for shooters who paper-tune tail-left (too stiff) on a 400 but don't want the full step to 500 — common around 48–52 lb of draw weight, on 55 lb recurves shooting 100 gr points with finger release, and on youth/transition bows where every half-grade of forgiveness matters. Availability is thinner than the standard ladder, so if you're building a dozen, verify stock for nocks and inserts in your shaft's inside diameter before committing. Measured at the bench, 450 should read 0.440–0.460″ — anything outside that band is mislabeled.

'55/70' (also written 55-70 or 5570) is the traditional wood-arrow grading: two deflection numbers in thousandths of an inch marking the shaft's spine range. A 55/70 Port Orford cedar deflects between 0.550″ and 0.700″ depending on which axis you measure — wood grain makes every shaft stiffer along one plane. The pair maps to roughly a 40–55 lb recurve or longbow. Choose within the range at the bench: test each shaft on both axes, note the stiff one, and orient that axis toward the bow. A dozen graded and axis-sorted 55/70 shafts will fly more consistently than an unsorted premium dozen — wood rewards measurement more than any carbon ever will. For comparison, the old two-number aluminum code (like 1816) is a different system: wall thickness and outside diameter, not spine.

One grade (400 → 340, or 340 → 300) equals roughly 100 points of deflection, 8–10 lb of draw-weight capacity, and 5–8% of shaft weight in the same family. Shoot a bow one grade off and the arrow flexes too much or too little around the riser: expect 4–6 inch field-point vs broadhead group splits at 20 yards, tail-left or tail-right paper tears, and erratic wind response. Half a grade — the difference between a 340 and a 350 label — is usually tunable with a 0.5″ cut or a 25 gr point change instead of buying different shafts. That's the practical meaning of 'spine difference': full grades change what you buy, half grades change what you adjust.

The 250–300 band is the heavy-hunting territory: 75–90 lb compounds, 650+ grain moose and dangerous-game builds, outsert-equipped extreme-FOC arrows carrying 200–300 grains up front, and many crossbow bolts. Between the two, 300 serves 70–80 lb bows (and 70 lb with 150 gr heads or 30″ draws); 250 serves 80–90 lb bows and the heaviest builds. Both classes run 10.5–13 GPI shafts, pushing total arrow weight past 550 grains — where momentum, not speed, does the work. If your bow is under 72 lb and your head under 125 gr, you almost certainly belong on 340/350 and should read the 300 vs 340 decision instead; buying into the 250/300 class 'for penetration' on a 65 lb bow just buys you a tail-left tear and a slower arrow.