Arrow setup analysis for a 28-inch arrow at 320 fps. Default specs: 381 gr arrow, 8.4 mm shaft diameter.
Total arrow mass for a 28" build: 381 gr = 238 gr shaft (8.5 GPI × 28") + 143 gr components (point + insert + nock + fletching).
KE: 86.7 ft·lbf — Momentum: 0.541 slug·ft/s
| Distance | Velocity | KE (ft·lbf) | Momentum (slug) |
|---|---|---|---|
| 0 yd | 320.0 fps | 86.7 ft·lbf | 0.541 |
| 10 yd | 314.0 fps | 83.4 ft·lbf | 0.531 |
| 20 yd | 308.2 fps | 80.4 ft·lbf | 0.521 |
| 30 yd | 302.4 fps | 77.4 ft·lbf | 0.512 |
| 40 yd | 296.8 fps | 74.5 ft·lbf | 0.502 |
| 50 yd | 291.2 fps | 71.8 ft·lbf | 0.493 |
This build pairs a standard-length cut with a high-speed compound launch. At 28 inches the shaft is the mainstream draw-length range, where most factory spine charts are calibrated and tuning is the most forgiving, and 320 fps is the kind of speed produced by aggressive, high-let-off compounds built for flat trajectories and short reaction windows. Together they finish at about 381 grains, which is what drives the kinetic energy and momentum figures in the table above.
Because this is a standard-length cut, this length sits near the centre of the spine chart, so published reference spines apply most directly. The launch matters too: with a high-speed compound launch, the dynamic-spine reaction is dominated by spine and rest tuning, because fast cams expose the smallest paper-tear and broadhead-flight errors. Pick a static spine that lands stiff once this 28" shaft and your point weight are factored in, then confirm it with bare-shaft or paper tuning.
At roughly 86.7 ft·lbf this is elk-class kinetic energy — this reaches elk-class energy, the territory recommended for elk, moose, and other heavy big game where maximum penetration is the priority. Keep in mind that a standard-length cut at 320 fps is only the starting point; broadhead choice and shot placement still decide the outcome more than the headline energy number.
A high-speed compound launch pushing roughly 381 grains yields about 0.541 slug·ft/s of momentum. That is heavy penetration potential: this is heavy-penetration momentum, the kind that drives through rib bone and dense muscle and resists deflection on angled shots. Momentum, more than raw kinetic energy, predicts how a 28" arrow holds up against bone and angled entry.
For a standard-length cut launched at 320 fps, dial in rest centre-shot and timing first, then verify broadhead flight against field points at distance. Spine and rest tuning, because fast cams expose the smallest paper-tear and broadhead-flight errors — so re-check the tear any time you change point weight, since that shifts the dynamic spine on a 28" shaft more than most archers expect.