Gyroscopic Stability of Open Tipped Match Style Rifle Bullets

Abstract

Earlier work has produced formulas for predicting stability of rifle bullets of near uniform density and also for plastic-tipped rifle bullets. These formulas have been shown to be accurate within 5%. However, the original Miller stability formula for metal bullets of near uniform density underestimates the stability of match style open tipped rifle bullets having a significant empty volume in the tip. This paper presents a new formula for accurately estimating the stability of these open tipped match style rifle bullets from parameters easily obtained such as the bullet mass, length, and depth of the empty space in the tip. The formula is tested by observations of whether bullets tumble and by measuring the aerodynamic drag vs. predicted stability of several bullets over a range of stabilities. In addition to confirmation in several test cases with original firing data, the new stability formula is validated by comparison with BRL spark range stability data for the 168 grain Sierra International in .308 to an accuracy of 2% for supersonic velocities (> M1.2).