Model arrow builds based on Dr. Ed Ashby's arrow lethality research. Calculate EFOC and Ultra-EFOC configurations designed for maximum penetration on large and dangerous game, with spine, mass, and broadhead matching guidance.
Enter your build. This calculator classifies your FOC against Ashby's penetration tiers and flags build issues that reduce terminal performance.
FOC% = ((A − L/2) ÷ L) × 100
Momentum = (grains × fps) ÷ 225218 in slug-ft/s. Ashby research prioritizes momentum and FOC together, along with structural integrity of the broadhead and shaft.
FOC classification against the framework from Dr. Ed Ashby's Arrow Lethality research (2005–2022).
| Tier | FOC Range | Class | Typical Build | Primary Use |
|---|---|---|---|---|
| Tier 1 | < 7% | Rear heavy | Standard light hunting arrow | Not recommended for hunting |
| Tier 2 | 7–12% | Standard | Factory hunting arrow | Deer at moderate ranges |
| Tier 3 | 12–19% | Heavy FOC | Brass insert + 125–150 gr head | Deer / elk / bear |
| Tier 4 | 19–25% | EFOC | 100+ gr brass + 150–200 gr head | Large game / penetration focus |
| Tier 5 | > 25% | Ultra EFOC | Steel insert + 200–300 gr head | Dangerous game / specialty |
Source: Dr. Ed Ashby, Bowhunting Foundation — Arrow Lethality research series. Ashby himself frames these as tendencies, not absolutes; individual animals and shot angles vary.
Successful Ashby-style builds share these traits:
| Target FOC | Shaft GPI | Insert | Broadhead | Total Weight |
|---|---|---|---|---|
| 12–15% | 8–9 | 50 gr brass | 125–150 gr | 450–520 gr |
| 15–19% | 9–10 | 75–100 gr brass | 150–175 gr | 520–600 gr |
| 19–22% (EFOC) | 10–11 | 100–125 gr brass/steel | 175–200 gr | 600–700 gr |
| 22–25% (EFOC) | 11–12 | 125–150 gr steel | 200–250 gr | 680–780 gr |
| 25%+ (Ultra EFOC) | 12–13 | 150–200 gr steel | 250–300 gr | 750–900 gr |
It is an FOC calculator framed around Dr. Ed Ashby's arrow lethality research. The math is the same ATA/AMO formula, but the interpretation uses Ashby's tiers — where FOC above 19% (EFOC) is associated with measurably better penetration on large game.
EFOC = Extreme Front of Center, typically FOC above 19%. Ultra-EFOC is above 25%. These classes were popularized through Ashby's writing and are adopted by heavy-arrow hunters who prioritize terminal performance over trajectory.
No. Whitetail deer are thin-skinned and lightly built relative to elk or buffalo. A standard 10–15% FOC hunting arrow delivers ethical kills on deer at normal distances. EFOC shines on large, thick-skinned game or angled shots.
Momentum (mass × velocity) correlates better with penetration depth than KE (mass × velocity²). Ashby's field data shows that heavy arrows with strong momentum carry through hide, muscle, and bone more consistently than light fast arrows with equal KE.
Single-bevel, cut-on-contact, fixed-blade broadheads in the 150–300 gr range. Robust construction matters more than cutting diameter. Popular choices include heavy Grizzly, Tuffhead, and VPA single-bevels.
Ashby's research suggests that higher arrow mass — commonly expressed as grains per pound (GPP) — supports deeper penetration. Many Ashby-inspired builds run 10–15+ GPP, which is significantly heavier than standard hunting setups at 6–8 GPP.
Yes. Dr. Ed Ashby's Bowhunting Foundation continues to publish follow-up studies, and his foundational work remains widely cited across heavy-arrow hunting literature. His framework is one of the most-cited sources on terminal arrow performance.