A Stability Formula for Plastic-Tipped Bullets Part 2: Experimental Testing

TL;DR

This paper experimentally tests a modified gyroscopic stability formula for plastic-tipped bullets, improving accuracy over the original Miller twist rule by accounting for the metal portion length, though limitations remain for certain core densities.

Contribution

It introduces an amended stability formula for plastic-tipped bullets and validates it through experimental testing, highlighting its accuracy and limitations.

Findings

The new formula improves stability predictions for certain plastic-tipped bullets.

It underestimates stability for bullets with less dense cores than the jacket.

Experimental results support the formula's applicability within specific density conditions.

Abstract

Part 1 of this paper describes a modification of the original Miller twist rule for computing gyroscopic bullet stability that is better suited to plastic-tipped bullets. The original Miller twist rule assumes a bullet of constant density, but it also works well for conventional copper (or gilding metal) jacketed lead bullets because the density of copper and lead are sufficiently close. However, the original Miller twist rule significantly underestimates the gyroscopic stability of plastic-tipped bullets, because the density of plastic is much lower than the density of copper and lead. Here, a new amended formula is developed for the gyroscopic stability of plastic-tipped bullets by substituting the length of just the metal portion for the total length in the (1 + L2) term of the original Miller twist rule. Part 2 describes experimental testing of this new formula on three plastic-tipped bullets. The new formula is relatively accurate for plastic-tipped bullets whose metal portion has nearly uniform density, but underestimates the gyroscopic stability of bullets whose core is significantly less dense than the jacket.