Shooting Position Stability Calculator

Position sets the base hold capability the calculator starts from — about 1.0 MOA for supported prone versus 6.5 MOA for unsupported standing — because a standing shooter's body has far less contact with the ground to cancel out wobble. That base MOA is what gets scaled by skill, wind, and heart rate and then converted directly into expected group size in inches at your target distance, so a position with 6x the hold-MOA produces roughly 6x the group size at the same range.

The calculator treats resting heart rates up to 70 bpm as having no measurable effect on hold, since pulse-driven muscle tremor is negligible at rest. Above 70 bpm, a penalty grows linearly toward 200 bpm, scaled to half your base position MOA at the top end — so elevated heart rate from exertion or adrenaline degrades a shaky standing position proportionally more than a already-stable bench rest.

It treats your expected group size as roughly two and a half standard deviations of shot dispersion, then runs that through a logistic-curve approximation of the normal distribution to estimate the odds a shot lands within a 20-inch-wide target. It's a simplified statistical stand-in for true ballistic dispersion, not a measured hit rate, so use it to compare setups against each other rather than as a guaranteed percentage.

This tool only models shooter-side wobble — how position, skill, wind-induced body sway, and heart rate widen your hold — not how wind physically pushes the bullet off course during flight or the rifle's own mechanical accuracy and ammunition consistency. For the bullet's actual wind drift and trajectory, you'd need to pair this with a dedicated ballistics calculator.