bulletDef.js

function calculateDeflection(twist, barrelLength, elevation, initialVelocity, distance, weight, humidity) {
	// Constants
	const GRAVITY = 9.81; // m/s^2
	const ATMOSPHERIC_DENSITY = 1.225; // kg/m^3
	const AIR_VISCOSITY = 1.78e-5; // Pa*s

	// Calculate the bullet's flight time and yaw angle
	const flightTime = distance / initialVelocity;
	const yawAngle = 0;
	b;

	// Calculate the deflection due to gravity
	const gravityDeflection = (GRAVITY * flightTime ** 2) / 2;

	// Calculate the deflection due to air resistance
	const airResistanceDeflection =
		(ATMOSPHERIC_DENSITY * initialVelocity ** 2 * Math.PI * yawAngle * weight) / (8 * AIR_VISCOSITY * barrelLength);

	// Calculate the total deflection
	const totalDeflection = gravityDeflection + airResistanceDeflection;

	return totalDeflection;
}

const twist = 12; // inches per turn
const barrelLength = 22; // inches
const elevation = 0; // meters
const initialVelocity = 863; // meters per second
const distance = 1000; // meters
const weight = 10.7; // grams
const humidity = 50; // percent

const deflection = calculateDeflection(twist, barrelLength, elevation, initialVelocity, distance, weight, humidity);

console.log(deflection);