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The U.S. Army Research Laboratory conducted a study to examine the effects of a small caliber (7.62-mm) cartridge s spit-hole on the interior ballistic performance of the cartridge. The performance metrics evaluated were cartridge pressure and muzzle velocity. The laboratory incorporated its custom breech apparatus that measures primer pocket pressure, and used standard midcase pressure measurements and high-speed imaging to evaluate early projectile motion out of a custom-built short barrel gun.

A ballistic coefficient (BC) can be determined by using two chronographs a measured distance away from each other and shooting a bullet so the velocity is measured by the two devices. Ballistic modeling software requires accurate measurement of ballistic coefficients to accurately predict downrange trajectories, wind drift, and retained energy. This article presents new measurements for 21 different bullets and shows that BCs can differ significantly from the claims of the manufacturer. These differences can cause significant differences in the predictions of ballistic modeling software. Evidence suggests that these variations are probably not due to excessive bullet yaw.

Recent requirements for hypervelocity projectile launch for strategic U.S. Army missions have led to the proposal of a variety of gun propulsion systems. Among these systems are those that utilize solid propellant along with electrothermal-chemical (ETC) augmentation. Advanced solid propellant systems with complex grain geometry and loading configuration are also being investigated. In response to this need, the U.S. Army Research Laboratory (ARL) has, for a number of years, engaged in the study of solid propellant ignition using a hot, low molecular-weight plasma generated by ETC means. In addition, ARL is developing an ETC modeling capability using the next-generation interior ballistics code, NGEN, and a series of experimental studies in a ballistic simulator to generate code validation data. The current report demonstrates progress for application of the NGEN code to solid propellant, direct-fire gun systems in which various propellant configurations (i.e., grains and disks) are combined into a single charge in order to obtain higher-loading densities. The charge is ignited using the efflux from an ETC plasma capillary made of polyethylene. Comparison with pressure data measured in a 25-mm ballistics simulator, filled with disks of JA2 propellant as the main charge and a small amount of inert grains as filler, provides validation of the NGEN model with respect to the representation of the plasma efflux from an ablation capillary, into the chamber, and around propellant disks.

Recent requirements for hypervelocity projectile launch for strategic U.S. Army missions have led to the proposal of a variety of gun propulsion systems. Among these systems are those that utilize solid propellant along with electrothermal-chemical (ETC) augmentation. Advanced solid propellant systems with complex grain geometry and loading configuration are also being investigated. In response to this need, the U.S. Army Research Laboratory, in cooperation with Paul Gough Associates, is developing the Next Generation Interior Ballistics model, NGEN. The goal of this project is the development of an advanced interior ballistics model for use in the design and investigation of both indirect-and direct-fire gun propulsion systems. The current report demonstrates progress for application of the NGEN code to solid propellant, direct-fire gun systems in which various propellant configurations (i.e., grains and disks) are combined into a single charge in order to obtain higher-loading densities. The charge may be ignited using either a conventional (Benite) or an ETC plasma capillary. These notional charges are being investigated to determine code performance and assess the need for code upgrades, as well as to investigate propellant ignitability with Benite and plasma sources. Comparison with pressure data measured in a 25-mm ballistics simulator, filled with inert disks and grains, provides validation of the NGEN model with respect to the representation of the plasma efflux from an ablation capillary, into the chamber, and around propellant disks.

There has been wide support for the continued reduction in weight of heavy armor combat systems. Of course no one is willing to give up performance with this reduction in weight. This program investigated the feasibility of utilizing Ti-6Al-4V as an alternate armor material for the Ml Abrams turret glacis as opposed to the presently utilized RHA steel. Two turret glacis test sections were fabricated from Ti-6A1-4V armor plate, and one was fabricated from RHA steel. These sections were ballistic tested vs. common threats. The weld joint design is described from a theoretical basis as well as functional performance. The ballistic results of all test sections are discussed in detail, and recommendations for future work are provided.

This report presents the results of a design study to replace the existing OH-58 C/A Main Rotor Blade with a Composite Rotor Blade. The effort consisted of a trade study phase and a preliminary design phase. The composite construction rotor blade defined in this report in whole or in part meets the defined improvement objectives in the areas of life cycle cost, performance, reliability and maintainability, radar reflectivity, and ballistic survivability.

A theoretical and experimental study was made to determine where a fixed length, constant diameter tube should be divided so that when one portion of the tube was used as a gun barrel and the remaining portion was used as a driver, the maximum projectile muzzle velocity would be obtained for a particular driver gas and initial projectile acceleration. Studies were made of several gas gun configurations, of 4-in. (10-cm) inside diameter and 100-ft (30- m) length, for muzzle velocities greater than 500 ft/s (150 m/s). Calculations were made by using the Lagrange theory for very low Mach numbers; the constant diameter, infinite reservoir theory for very high initial accelerations; and the Pidduck-Kent theory for other regimes. Experimental results and theoretical predictions are compared for several gun divisions, helium and nitrogen drivers, and initial accelerations from 200 to 5000 g. For improved gun utilization, gun configurations are suggested to reduce exit gas pressure, to reduce the quantity of driver gas required, and to ease operation and improve (statistical) utilization of the gun without unduly affecting muzzle velocity. Although the results obtained are specific to the Harry Diamond Laboratories 4-in. gas gun, computer programs are included that may be applied to other gun geometries.

Test firings of prototype fin- and flare-stabilized 25 mm training rounds were conducted. The fin-stabilized rounds were found to be capable of fulfilling all of the training round ballistic requirements. The flare- stabilized rounds were studied as a possible lower cost alternative. Initially, a large angle flare design, similar to existing tank gun training round, was tested, but data showed the configuration drag coefficient was too high. Subsequent computer predictions indicated that a small angle flare would have significantly lower drag and sufficient stability for flight. A four-degree flare was fabricated and fired, confirming the drag and stability predictions.

Recent activity with regard to development of a pulsed laser, remote crosswind measurement system is described. Work was concentrated on system improvements and testing. The improvements included the ability to directly measure the average received intensity, a method of aligning the two laser beams so that they are colinear; normalization to compensate for turbulence strength and laser coherence, and accurate automatic gain calibration. Testing included a comparison of the pulsed crosswind system with in situ measurements and cw measurements of the time delayed statistics.

A prototype instrument to determine the orientation of a projectile in free flight (i.e., roll, pitch and yaw angles) was developed at Boeing and used to perform test at the U.S. Army Ballistic Research Laboratory (BRL) at Aberdeen Proving Ground MD. The instrument incorporated two visible gas lasers (to provide a two color collimated illuminating beam) and a pair of galavanometer beam deflectors from the detected light reflected of the output beam. All three angles can be determined from the detected light reflected by a retroreflector/hologram combination mounted on the projectile. The prototype instrument was designed to make three-axis angle measurements on in-flight or in-bore spinning or non-spinning projectiles, and to make two-axis angle measurements of gun tube motion. Tests were performed by both Boeing and BRL personnel at the Aerodynamics Range at BRL during a two-week period in August 1985. The test instrumentation was then left at BRL for additional testing by BRL personnel.

Studies were directed at the deflagration of heterogeneous, condensed media. Relations among ballistic properties were studied; generalized relations were derived and existing relations for testing the consistency of data from ballistic test motors were shown to be general to small error; errors in the recent literature were corrected. A new device for characterizing the ballistic properties of condensed media at high pressure with strands was devised and explored analytically. Self-pressurized constant pressure operation was shown along with capability to control the pressure level with a simple bang-bang control system. Special configurations to provide direct little difference measurements of ballistic sensitivities were presented. The Deur/Glick serial sandwich model for heterogeneous propellant combustion was modified to overcome the 'continuation' problem implicit in that model. Results showed ignition delays of correct magnitude and, with physical reasoning, demonstrated that the ZN methodology cannot be applied to heterogeneous propellants in its present form. Keywords: Solid rocket propellants, Solid propellant rocket engines.

This report summarizes Ballistic shock test results on 1 inch and 3/4 inch homogeneous armor 'H' plates welded with austenitic electrodes and tested at Aberdeen Proving Ground.

The tests reported here were conducted to determine the effects produced on the ballistics of a liquid monopropellant round by advancing the point of venting of the primer within the propellant column. The tests were conducted with two case configurations in which the L/D ratios of the propellant columns were approximately 3.4 and 5.0. As the point of venting was advanced, muzzle velocity increased in rounds with the L/D ratio of 5.0, but decreased in those with the L/D ratio of 3.4. The amount of unburned propellant remaining in the case after firing increased in both case configurations. In both configurations, the pressure curves were transformed from curves with two distinct pressure peaks, through stages approximating plateau configurations, to curves with one well defined pressure maximum.

Closed-breech interior-ballistic equations were modified for predicting the performance of reactionless launchers. Test firings were made using two reactionless launchers of the Davis Gun type. Direct and high-low launchers were considered. The test firing data was compared with the curves obtained from an analog computer. Using the differences noted, certain factors of the original equations programmed into the computer were varied in order to bring the computer curves into close agreement with actual test results. These factors included heat loss coefficient, initial charge burnt, and in the case of the high-low gun the effective mean impetus of the propellant during the ballistic cycle. It was concluded that the knowledge gained with the computer can be used to optimize the performance of reactionless systems.

A new single-stage, high-pressure, stainless steel, light-gas gun 30 ft long with a 1 3/8-in. bore has been designed and built at DOFL. This gun has driven a 6-gm mass at velocities above 5000 fps. With alterations made to heat the driver section, it is expected to give velocities of over 8000 fps and make possible impact shock pressures of more than 1-megabar. A comparison of the measured and computed projectile velocities at room temperature as well as higher temperatures is included.

A feasibility study of a smoke or vapor stream system to function in the nose cone of a fin-stabilized round was conducted. The conventional base-located system could not be used because (a) the round contained a discarding sabot mechanism, and (b) the vibration, jolt, and dust following the discharge of the large vehicle-mounted gun would cause the gunner to momentarily lose sight of the missile. Hence, a persistent trail observable by daylight was needed. Titanium tetrachloride was tried because, on exposure to air, it forms dense white clouds of titanium hydroxide. However, the corrosive properties of this material made it difficult to package. Since calculations indicated that nose temperatures exceeding 300 deg C would be attained during projectile flight, a new approach using a heat sensitive initiator was formulated. Diazodinitrophenol (DDNP), which ignites after 0.25 second of flight (200 deg C) was pressed into the nose cone tip assembly. A conically shaped red smoke composition was inserted directly behind the DDNP. Two holes drilled near the apex of the cone body allowed the generated smoke to escape. This approach worked satisfactorily in static tests. In ballistic tests, however, the smoke composition was ejected as a puff of red smoke with no streaming.

Variable-resistance strain gages were used to study the operating characteristics of a light-gas gun. Gages were cemented on the outer surface of the gun at several locations, in order to determine chamber pressure, piston velocity, and pressures in the central breech. The high-pressure transition section deformed plastically in most rounds, and a method is suggested for estimating maximum pressures from strain-time records. Results are given for various helium pressures and powder charges.

The work of design and fabrication of three Laser Telemeter Units having 18 channels of IRIG telemetry and using a PPM GaAs Laser is described. After a general discussion of the principles of telemetry and of the signal-to- noise enhancement properties of FM, PPM, and PCM systems, a detailed discussion of the electrical and of the mechanical design is presented.

Techniques were developed to launch ultralightweight models (i.e., densities on the order of 1 lb/3 cu. ft.) from a two-stage light-gas gun. To date, spheres and cones have been launched with some success. The purpose of the development was to determine whether useful aerodynamic data (e.g., sphere drag) could be obtained in a short aeroballistic range at pressures on the order of 0.01 mm Hg. A number of spheres were launched in support of this effort, some at pressures as low as 0.03 mm Hg. There is good agreement between these measurements of sphere drag coefficient and those produced in low-density wind tunnels. The application of this technique to a longer range having a lower pressure capability, say, 0.001 mm Hg, would permit measurements to be made in the near-free-molecule flow regime.

Various aspects of the perforation of thin targets by high speed fragments were investigated. A fragment projector yielding compact steel fragments having a velocity of 3.17 km/sec and a mass of .0234 g was generally used for experimental studies. Design features of this projector are presented with methods of attaining higher velocities. The volume and shape of craters produced in lead at 60 degrees obliquity by fragments having a velocity of 4 km/ sec are compared with the characteristics of craters produced at impact velocities of 3 km/sec and 5 km/sec.