Supersonic Bullet Research Articles

Investigation of nonlinear propagation effects on sound from supersonic bullets

ISO standard 17201-4 is a calculation method for sound levels generated by supersonic bullets. The standard takes into account nonlinear propagation effects, including broadening of a sound pulse with increasing propagation distance. Two elements of the ISO method are investigated in this paper: i) the accuracy for various Mach numbers, and ii) the effect of noise barriers. For the first element, calculation results are compared with measurement results. In general the agreement is good, but large deviations occur at Mach numbers near unity. Calculation parameters were varied in order to find an explanation for the deviations. For the second element, propagation paths along the horizontal top edge and the vertical side edges of a barrier of finite length are considered. For the path over the top edge, a possible approach is developed to account for the expected reduction of nonlinear propagation effects in the shadow region behind a barrier. For the paths along the vertical side edges, a simulation model with a dense distribution of point sources is employed. The three propagation paths are explained in terms of pairwise cancellation of Fresnel zones. The results of the simulation model are compared with results of an engineering model.

Numerical Study on a Supersonic Flow around a Bullet

In this research paper, a numerical analysis in Computational Fluid Dynamics uses the Finite Volume Method to visualize the external flow characteristics over a bullet speeding at Mach 2.0. The simulation results evaluate the experimental drag coefficient of the supersonic bullet airflow in a wind tunnel. The numerical simulation assumes that the inviscid model remains non-rotating. The generation of the mesh geometry varies between Coarse, Medium, and Fine types, and proper selection of the grid density improves the accuracy of the numerical result. The Fine Quadrilaterals mesh of 150,000 elements achieved considerable punctuality along with the numerical method of the second-order linear differential equations. The drag coefficient value of 0.222 gives a 0.9 percent error relative to the attained experiment value. The Mach number, pressure ratio, and flow simulation velocity contours obtained with ANSYS FLUENT software represent the validation of the experimental data with numerical analysis method in a typical fluid mechanics problem.

Why Did the Earwitnesses to the John F. Kennedy Assassination Not Agree About the Location of the Gunman?

Earwitnesses to the 1963 assassination of President John F. Kennedy (JFK) did not agree about the location of the gunman even though their judgments about the number and timing of the gunshots were reasonably consistent. Even earwitnesses at the same general location disagreed. An examination of the acoustics of supersonic bullets and the characteristics of human sound localization help explain the general disagreement about the origin of the gunshots. The key fact is that a shock wave produced by the supersonic bullet arrived prior to the muzzle blast for many earwitnesses, and the shock wave provides erroneous information about the origin of the gunshot. During the government's official re-enactment of the JFK assassination in 1978, expert observers were highly accurate in localizing the origin of gunshots taken from either of two locations, but their supplementary observations help explain the absence of a consensus among the earwitnesses to the assassination itself.

The reduction of gunshot noise and auditory risk through the use of firearm suppressors and low-velocity ammunition

Objective: This research assessed the reduction of peak levels, equivalent energy and sound power of firearm suppressors. Design: The first study evaluated the effect of three suppressors at four microphone positions around four firearms. The second study assessed the suppressor-related reduction of sound power with a 3 m hemispherical microphone array for two firearms. Results: The suppressors reduced exposures at the ear between 17 and 24 dB peak sound pressure level and reduced the 8 h equivalent A-weighted energy between 9 and 21 dB depending upon the firearm and ammunition. Noise reductions observed for the instructor’s position about a metre behind the shooter were between 20 and 28 dB peak sound pressure level and between 11 and 26 dB LAeq,8h. Firearm suppressors reduced the measured sound power levels between 2 and 23 dB. Sound power reductions were greater for the low-velocity ammunition than for the same firearms fired with high-velocity ammunition due to the effect of N-waves produced by a supersonic bullet. Conclusions: Firearm suppressors may reduce noise exposure, and the cumulative exposures of suppressed firearms can still present a significant hearing risk. Therefore, firearm users should always wear hearing protection whenever target shooting or hunting.

Curvilinear trajectory estimation of a supersonic bullet using ballistic shock wave arrivals at asynchronous acoustic sensor nodes.

The trajectory of a supersonic bullet, which is subjected to drag and gravity, is curvilinear and the supersonic flight of the bullet generates a ballistic shock wave (SW). A model for the differential time of arrival (DTOA) of the SW at a pair of acoustic sensors is derived for a given bullet trajectory, which is fully described by seven parameters including the drag coefficient exponent and ballistic constant of the bullet. Assuming that the drag coefficient exponent is 0.5, the DTOA model is used to develop a nonlinear least-squares (NLS) method to estimate the other six trajectory parameters using DTOA of SW measurements from each node (which comprises a small acoustic sensor array) of an asynchronous sensor network. The position of the shooter and the muzzle speed of the bullet are then determined by tracing the estimated bullet trajectory back to topographic or man-made obstructions on a digital map. The effectiveness of the NLS method is verified using simulated data for different types of real bullets, and the error standard deviations in the parameter estimates are close to the Cramer-Rao lower bounds.

Comparison of supersonic bullet ballistic models for accurate localisation of small arms fire

This study evaluates and compares the accuracies of five different ballistic models in predicting the speed profile of a supersonic bullet using radar measured speed data for 36 types of bullets. Each of the five ballistic models is parameterised by a ballistic constant and the muzzle speed of the bullet. In practice, each of these two parameters spans a wide range of values because of the large number of different bullet types that are available for use in a variety of applications. For a given bullet type, the bullet's ballistic constant and muzzle speed are determined by fitting the ballistic model to the data in a least-squares (LS) sense, and the root-mean-square (RMS) and maximum absolute (MA) deviations of the LS fit of the model from the data are computed. The best ballistic model (out of the five) is the one that has the smallest RMS and MA errors for the maximum number of bullet types. This ballistic model has been applied to accurate ranging of small arms fire using a single sensor node, with and without a priori knowledge of the model parameters, and its effectiveness for both cases is demonstrated using real data recorded from a field experiment.

Factors affecting sound exposure from firing an SA80 high-velocity rifle

The effect of distance on the peak sound pressure level and sound exposure level from an SA80 rifle has been investigated. Sound pressure waveforms were measured in two directions from the gun: downrange, from 50m to 300m, and to the left-hand side, from 0.3m to 32m. Some additional measurements were made to the right of the gun. Measurements made downrange showed three distinct features of the waveform; the shock wave from the supersonic bullet, the reflection from the ground, and the muzzle blast. The time elapsed between the shock wave and the muzzle blast increased with increasing distance: 94ms for a distance of 50m, and 507ms for a distance of 300m. The highest peak sound level downrange from a single round was between 151dB(C) and 148dB(C) at distances from 50m to 300m, and varied little if at all with distance. To the left of the gun, the peak sound pressure level of 161dB(C) at 0.3m reduced to 128dB(C) at 32m. The peak sound pressure level was estimated to be 137dB(C) at a distance of approximately 20m to the left-hand side. Hearing protection must therefore be worn by anyone closer than 20m to a person firing. The peak sound pressure level was estimated to be 135dB(C) at a distance of approximately 25m and therefore hearing protection is recommended at distances of up to 25m. The sound exposure level of 98dB(A) at 20m indicated that an observer at this distance could hear about 1440 rounds without hearing protection before the noise exposure reached the upper exposure action value specified in the Control of Noise at Work Regulations 2005. Peak sound pressure levels were on average 2.4dB higher at the left ear compared with the right ear.

Single-shot compressed ultrafast photography at one hundred billion frames per second.

The capture of transient scenes at high imaging speed has been long sought by photographers, with early examples being the well known recording in 1878 of a horse in motion and the 1887 photograph of a supersonic bullet. However, not until the late twentieth century were breakthroughs achieved in demonstrating ultrahigh-speed imaging (more than 10(5) frames per second). In particular, the introduction of electronic imaging sensors based on the charge-coupled device (CCD) or complementary metal-oxide-semiconductor (CMOS) technology revolutionized high-speed photography, enabling acquisition rates of up to 10(7) frames per second. Despite these sensors' widespread impact, further increasing frame rates using CCD or CMOS technology is fundamentally limited by their on-chip storage and electronic readout speed. Here we demonstrate a two-dimensional dynamic imaging technique, compressed ultrafast photography (CUP), which can capture non-repetitive time-evolving events at up to 10(11) frames per second. Compared with existing ultrafast imaging techniques, CUP has the prominent advantage of measuring an x-y-t (x, y, spatial coordinates; t, time) scene with a single camera snapshot, thereby allowing observation of transient events with temporal resolution as tens of picoseconds. Furthermore, akin to traditional photography, CUP is receive-only, and so does not need the specialized active illumination required by other single-shot ultrafast imagers. As a result, CUP can image a variety of luminescent--such as fluorescent or bioluminescent--objects. Using CUP, we visualize four fundamental physical phenomena with single laser shots only: laser pulse reflection and refraction, photon racing in two media, and faster-than-light propagation of non-information (that is, motion that appears faster than the speed of light but cannot convey information). Given CUP's capability, we expect it to find widespread applications in both fundamental and applied sciences, including biomedical research.

Supersonic bullet shadowgram in air showing bow shock and turbulence

Supersonic bullet <i>shadowgram in air showing bow shock and turbulence</i>

A model-based acoustical signal processing method for the passive ranging of sniper gunfire

Acoustically, sniper gunfire is characterized by a muzzle blast caused by the discharge of a bullet from a rifle and a ballistic shock wave emitted along the trajectory of a supersonic bullet. The location of the firing point can be estimated by using a small microphone array to measure the differences in the angles- and times-of-arrival of the muzzle blast and shock wave. Traditionally, the bullet is assumed to travel at constant speed along its trajectory which, in practice, can lead to significantly biased range estimates. This problem is solved by invoking a physics-based model to describe the deceleration of the bullet along its trajectory. The ballistic model parameters are the initial (or muzzle) velocity and ballistic constant of the bullet, which are assumed to be known a priori. The performances of the traditional and model-based methods for ranging the point of fire are evaluated using 2,500 rounds of 5.56 and 7.62 mm ammunition fired at ranges of 75, 175, 275, 375 and 475 m under two (low and high) wind speed regimes. It is found that the localization errors of the model-based method are smaller by an order of magnitude when compared with those of the traditional method.

The shock wave-based acoustic sniper localization

Acoustic signals of small arms’ fire, the muzzle blast and the shock wave generated by a supersonic bullet in air are difficult to mask and can be exploited for localization of the hidden sniper. The problem is formulated for the curvilinear bullet path of unknown parameters (velocity and acceleration) in a system of nonlinear equations that can be solved numerically. A successful iterative solution is presented in a computed example based on technically feasible measurements of the shock wave arrival times at a system of nine omnidirectional microphones distributed in the protected area.

Ferret and its applications

Ferret is an acoustic system that detects, recognizes and localizes the source and direction of small arms fire. The system comprises a small array of microphones and pressure sensors connected to a standard PC-104 computer that analyzes, displays, reports and logs the parameters of a recognized shot. The system operates by detecting and recognizing the ballistic shock wave created by the supersonic bullet, combined with the muzzle blast wave propagating from the weapon. The Canadian Land Force Test and Evaluation Unit evaluated a vehicle-mounted version of the system and recommended deployment of the system during peacekeeping missions. The system is the result of a collaborative effort between Defence R&amp;D Canada and MacDonald Dettwiler and Associates. This presentation describes the hardware and software components of the system along with the current and future applications of the system.

Full-scale schlieren visualization of supersonic bullet and muzzle blast from firing a .30-06 rifle

Full-scale schlieren visualization of supersonic bullet and muzzle blast from firing a .30-06 rifle

Trajectories of projectiles in air for small times of flight

Angle of departure, angle of fall, and the position of the summit of trajectories in air are calculated with neglect of the effect of the air on the fall from the line of departure. Experimental information required is times of flight against range or remaining velocities against range. Calculated values are compared with observed values for a supersonic bullet.