The rifling is applied to most of the conventional gun barrels to stabilize the projectile using the spin. The rifling force (torque) acting on the projectile inside the barrel also wears the rifling itself and shortens the gun lifespan. To reduce the rifling wear, the increasing rifling angle is designed. The starting-part low angle decreases the rifling force while the increased muzzle angle creates the required projectile spin. With the advance of the computer-aided design and manufacturing, a smooth rifling curve is introduced using the Fourier functions. The method shows a high performance in decreasing the maximum rifling forces, but applying the design constraints is limited due to the sinusoidal features of Fourier functions. In this research, a node-point-based rifling-angle design method is introduced. The optimization algorithm and the interpolation method are used to create the smooth profile from the discrete parameters. With the piecewise cubic hermite interpolating polynomial (PCHIP) monotonicity, it is possible to apply various constraints easily while maintaining the design feasibility. To verify the performance, the design results and the comparisons with the previous methods are presented.