ArrowForge uses a physics-based ballistics engine and a context-aware Build Match Score to evaluate every arrow build — no black boxes, no guesswork.
Most archery calculators show you a number — spine chart deflection, FOC percentage, kinetic energy — and leave you to interpret it. ArrowForge instead asks a harder question: how well does this specific build match this specific archer, bow, and goal?
A 400-grain arrow flying at 310 fps is excellent for a 3D competitor shooting 50 yards in the open. It is a questionable choice for a bowhunter picking their way through timber at 25 yards after a 600-pound black bear. Same arrow, same bow, different score — because context changes everything.
The Build Match Score translates that context into a single 0–100 number with two clear sub-categories: Forgiveness and Tuning Match.
The overall score is a weighted average of Forgiveness and Tuning Match. The weights shift based on what the archer is working toward:
| Archer application | Forgiveness weight | Tuning weight |
|---|---|---|
| Bowhunting | 60% | 40% |
| Competition / Target | 35% | 65% |
| Training / Other | 50% | 50% |
A hunter's score leans on forgiveness because a hunting shot is rarely from a bench — it involves adrenaline, an awkward angle, a hard hold at full draw. A target shooter's score leans on tuning because at 50 meters, a mismatched spine or poor FOC will show up in every arrow.
| Score | Band | What it means |
|---|---|---|
| 85–100 | Excellent | Build is well-matched; small gains possible but this setup is working |
| 70–84 | Good | Solid build with room to improve one or two factors |
| 50–69 | Fair | Noticeable gaps — tuning changes would help meaningfully |
| 0–49 | Low | Build is mismatched for stated goal or bow; review recommended |
Forgiveness measures how much margin for error is built into the setup. A forgiving build groups well even on a slightly off shot. An unforgiving build demands perfection every time.
Up to seven factors contribute to the Forgiveness score. Their weights shift based on the archer's farthest practice distance and target species — because what matters at 20 yards in the timber is different from what matters at 70 yards in the open West. Two factors are context-specific: flatness only activates at mid and long range; arrow weight only activates for dangerous-game pursuits.
GPP is total finished arrow weight divided by draw weight. It is the single best predictor of how the arrow will behave at the shot: too light and the bow works against itself (excess vibration, poor efficiency, hard on equipment); too heavy and the arrow loses speed and trajectory. Compound optimal range is 5.5–8.0 GPP; traditional bows run 7.5–9.5 GPP. GPP carries the most weight in short-range and big-game scoring where penetration and controlled energy delivery matter most.
A composite check across three independent factors: arrow speed (does the build generate enough velocity to stabilize the shaft?), FOC (is the center of mass forward enough to keep the arrow nose-forward through the shot?), and GPI — grains per inch — (is the shaft heavy enough per unit length to resist wind deflection without being too stiff to tune?). All three must be in range for full marks; partial credit is awarded proportionally.
For compounds: let-off percentage. A 90% let-off holds 10% of peak weight at full draw — a major factor for a bowhunter waiting for a shot opportunity. For recurves and traditional bows: bow length. A longer bow draws a shorter string angle at the fingers, reducing torque and improving consistency.
The distance from the grip throat to the bowstring at rest. Shorter brace heights increase the power stroke and arrow speed — but the arrow stays on the string longer, meaning any hand movement during the shot is transmitted to the arrow. Most modern compound bowhunters favor 6.5 inches or more. Below 6.0 inches, the margin for error shrinks substantially.
Shaft diameter. Smaller-diameter arrows (4mm / 0.204") punch through air more cleanly and drift less in wind — meaningful at distance. At close range, this factor carries almost no weight in the score. At 60+ yards, it becomes significant. The scoring penalizes large-diameter shafts at long range because physics does.
At mid and long range, the cost of misjudging distance depends almost entirely on how flat the arrow flies. A flatter trajectory means a smaller drop difference between, say, 55 and 60 yards — so a range-estimation error costs less. ArrowForge measures the extra drop from 20 to 60 yards and scores it against a physics-matched baseline for the bow type (compound anchor: 4.0 ft; recurve anchor: 10.0 ft). This factor carries 10% weight at mid range and 20% at long range. At short range the drop differential is too small to matter, so the factor is inactive and its weight redistributes to the other five.
For dangerous-game pursuits — brown bear, bison, cape buffalo — total finished arrow weight becomes a standalone factor. Heavy arrows carry momentum that light-and-fast setups cannot match at bone. This factor is inactive for most hunting and all target applications; it only enters the score when the target species demands it.
Tuning Match evaluates whether the arrow's dynamic spine, weight, and (when known) measured speed are correctly dialed for the specific bow.
ArrowForge computes effective draw weight — the load the bow actually exerts on the shaft given draw length, point weight, and total arrow weight — and then checks whether the selected shaft's rated spine sits within the expected range. This is not a simple chart lookup: effective draw weight shifts 2.5 lbs per inch of draw length away from 28" and 0.15 lbs per grain of point weight away from 100 grains. Spine carries 50–62% of the Tuning Match score depending on whether a measured arrow speed is available.
GPP appears in both Forgiveness and Tuning Match because it reflects two different things. In Forgiveness, it is about energy delivery and equipment stress. In Tuning Match, it is about whether the arrow's mass is in the range where the bow can efficiently transfer energy without oscillation. An arrow that is too light for the bow cycles poorly out of the shot; too heavy and it loses the energy advantage of the bow's draw weight.
If the archer enters a measured arrow speed, ArrowForge compares it to the expected velocity for that bow, draw length, and arrow weight. A well-tuned bow running within 25 fps of predicted velocity scores full marks. Larger gaps suggest a timing, cam, or limb issue — or that the entered specs don't match what's actually on the bow. This factor contributes 20% of Tuning Match when present.
The Build Match Score is built on top of a deterministic ballistics engine that runs the same physics equations used in external ballistics, adapted for arrows.
KE (in foot-pounds) and momentum (slug·ft/s) are calculated at the muzzle and at the target using the arrow's measured or estimated velocity and weight. Momentum is the better predictor of penetration on large game — it measures how much the arrow resists being stopped — while KE is a better indicator of how much energy is available at impact. ArrowForge reports both and evaluates them against established thresholds for small game, deer, elk, and dangerous game.
Arrows shed speed rapidly compared to bullets — a typical hunting arrow loses 15–25% of its velocity by 40 yards. ArrowForge models this with an exponential decay that accounts for arrow weight: heavier arrows carry their velocity better than light ones despite starting slower. The formula: impact velocity = launch velocity × e^(−0.532 × range / weight). This constant was calibrated against published arrow flight data.
Drop is calculated using a time-of-flight model. ArrowForge measures the additional drop from 20 yards to 60 yards — the extra drop relative to the near pin — because this is what drives sight tape spacing and hold-over decisions in the field. Flatter trajectories reduce the cost of a range estimation error, which matters most at distance and least at close range.
This flatness measurement also feeds directly into the Forgiveness score at mid and long range. It is how ArrowForge quantifies range-estimation-error forgiveness as a scored build attribute: a build that prints a 4.0 ft extra drop forgives yardage miscalls that would cost 8.0 ft of drop on a slower setup. The Trajectory tile displays the standalone flatness verdict; the Forgiveness score weights it alongside the other active factors for the archer's distance and pursuit context.
Elevation changes air density, and air density changes how fast an arrow slows down and drops. ArrowForge corrects for elevation using a standard barometric formula accurate to within 1% up to 16,000 feet — relevant for bowhunters in the Rockies or high-desert hunts where a sea-level sight tape will print several inches low at distance.
The score is a tool, not a verdict. ArrowForge will tell you that your brace height is below the preferred band — it will not tell you to change your bow. It will flag an underspined setup — it will not prescribe a specific shaft by brand. The recommendations point toward levers the archer controls: point weight, cut length, insert weight, draw length confirmation. Equipment decisions belong to the archer and their bow technician.