Every gun starts with an idea, and that alone is waterproof.
The simple model treats a band like a spring: force rises in a straight line with stretch, and stored energy is just a triangle under that line. Real latex doesn't behave that cleanly. It's viscoelastic — stiffer the faster you stretch it, and it gives back less energy than you put in. Two formulas, two very different answers:
The gap between those two numbers is the whole reason "just add more bands" stops paying off the way the spec sheet suggests it should.
Load a band and release it, and the loading curve and the unloading curve don't trace the same path — they form a loop. The unloading curve sits below the loading curve at every point in between, which means some of the energy you put in during the draw never comes back out on the shot. That gap is hysteresis loss, and on amber latex it typically runs 15–20% per cycle. Hold a gun loaded too long before the shot and a second effect, stress relaxation, stacks on top of it — tension can bleed off another 10–15% the longer the band sits stretched.
A traditional muzzle-tied band is fully slack the instant the shaft clears the muzzle — right when you'd want the most push left. A roller, anchored back along the barrel through a pulley, keeps the band under real tension across nearly the whole stroke instead of bleeding it off early. The force doesn't ramp in a straight line — it climbs fast off the bottom, holds flat through the middle of the stroke, then finishes near peak. More area under that curve means more energy delivered to the same shaft over the same length of gun.
Put rough numbers on the two layouts above and the gap shows up in real units, not just shape-of-curve. Same stock, same general band stretch — the roller's longer effective power stroke is what makes up for running fewer, lighter bands.
| Spec | Traditional | Roller |
|---|---|---|
| Stock Length | 58 in | 58 in |
| Band Count | 3 | 2 |
| Power Stroke | 34 in | 46 in |
| Peak Band Force | ~390 N | ~430 N |
| Potential Band Energy (F × D) | ~340 J | ~500 J |
Drag underwater rises with the square of speed, so a shaft doesn't just slow down faster as it goes quicker — it hits a hard velocity ceiling no matter how many bands get added behind it. Past a certain point, each extra band buys a shrinking return, because the shaft simply can't move fast enough to use the extra force before drag eats it.
| Band Setup | Energy In | Efficiency | Energy to Shaft |
|---|---|---|---|
| Dual 14mm, Small ID | 480 J | 88% | 422 J |
| Triple 14mm, Small ID | 720 J | 81% | 583 J |
| Quad 16mm, Standard | 1,100 J | 62% | 682 J |
| Hexa-Bands | 1,550 J | 39% | 604 J |
That's drag on the shaft. There's a second, less-talked-about ceiling: drag on the band itself. A stretched band doesn't snap back instantly — water resistance acts on the rubber too, and the material has its own physical limit on how fast it can contract. Past some band count, the bottleneck may not be the shaft at all; the bands could be racing against their own maximum contraction speed before the shaft has even cleared the barrel. Nobody's pinned this down precisely — it's a high-speed-camera question, not a spreadsheet one — but it's worth knowing the ceiling probably has two causes stacked on top of each other, not one.
Kinetic energy scales with velocity squared but only linearly with mass, so a lighter shaft driven by the same bands moves faster — but past a point, a shaft too light just gets outrun by its own bands and loses accuracy and penetration. Matching shaft weight to band power, not maxing either one out independently, is what actually gets more energy on target.
What this means for a Booth gun: it's why bands here are sized to the diver and the target instead of just stacked thicker, why the wishbone is a Dyneema double-wrap instead of a single line, and why shaft weight gets matched to the rigging rather than maxed out for show. The spec sheet is the output of this math, not the other way around.