7.62mm, Lethal Limited Range Round For USCG Informational Brief for NDIA 2011 25 May 2011
7.62mm, Lethal Limited Range Round For USCGInformational Brief for NDIA 201125 May 2011
Project Overview & Objectives
Overview
• JSSAP funded effort for USCG
• 7.62mm Lethal Limited Range Round
• For use in harbor security applications.
Objectives
• Reduced maximum range
• Engage and defeat
Customer Requirements
M80L2R2• Defeat 1/4 inch of mild steel at 200 meters, at a 45-degree angle
• Match trajectory of M80 out to at least 400 meters.
• Capable of defeating soft target out to at least 400 meters.
• Maximum range of 2000 Meters (1500 Meters desirable)
• Capable of being fired from an M14 rifle and M240 Machine Gun
Value to Warfighter
• Operational environment close to civilian populace
• Lethal force often necessary to accomplish missions
• Use of Small Arms at times is restricted due to potential risk to civilians
• Reduced range ammunition will enable USCG to engage targets
Briefing Overview
• Project history
• Added/optimized features and how they were evaluated
• Current projectile design performance
2007
2008
20092010
DESCRIPTION
FY11 Tasks
• One piece • Solid Brass• Cuts along ogive• Standard 7.62 x 51mm Case & Primer• SMP-843 Propellant
• Spark Range Test• Dispersion @ 400m• Radar Test• CFD Study• Updated design• Manufactured projectiles• Charge Establishment • Evaluated Penetration• Entire Cartridge Salt-Fog Test• Radar Test ( w/ & w/o salt-fog exposure)• Analyze & Document Results
Project History
Base
CannelureOgive Cut Depth
Optimized/Added Features that Affect Max Range
V
Flat Base Round Base
Projectile (M80) Base Geometry Computational Fluid Dynamics Study
• Compared aerodynamics of flat base vs. round base M80 • Validated CFD generated static coefficients with spark range data (BRL-MR-1833) • Base shape changes wake vortex formation and pressure distribution
Flat Base Round Base
0.45
0.50
0.55
0.60
0.65
0.70
0.75
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
Bas
e P
ress
ure
/ Atm
oshp
eric
Pre
ssur
e
Base Location / Base Radius
Base Pressure Distribution
Round Base
Flat Base
Projectile (M80) Base Geometry and Drag
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.25 0.45 0.65 0.85 1.05 1.25 1.45 1.65 1.85 2.05 2.25
C D
Mach
Spark Range
CFD: Round Base
CFD: Flat Base
Cannelure and Drag
0.000
0.050
0.100
0.150
0.200
0.250
0.300
0.350
0.400
0.450
0.500
0.000 0.500 1.000 1.500 2.000 2.500 3.000
CD
Mach Number
M80 ball with cannelure
M80 ball without cannelure
Observed Modal Arms Damping at ARL Spark Range Test
λF > 0 and λS > 0 (Shot 32412, Mach 0.74)
•Yaw damps out at muzzle velocity• Yaw increase at Mach .75
(Shot 32421, Mach 2.6)λF < 0 and λS < 0
• 0.27” total thickness• Glass 0.115”• Laminate 0.04”• Glass 0.115”• Meets SAE Z26.1 standards• 50m (2800 ft/s)
L2R2 vs. Automobile Windshield Glass
400m Velocity (1800 ft/s)
L2R2 vs. 20% Ballistic Gelatin
50m Velocity (2800 ft/s)
Entire Cartridge Salt-Fog Humidity Test
0
500
1000
1500
2000
2500
3000
3500
4000
4500
-2000 -1500 -1000 -500 0 500 1000 1500 2000
Rang
e, m
Deflection, m
L2R2
Max Range Impact Area (salt-fog treated/untreated)
L2R2 Impact Area on M80 Safety Fan
Salt-Fog treated rounds travelled farther than untreated rounds
2000m
400m Dispersion Results
-20
-10
0
10
20
30
40
50
0 5 10 15 20 25 30 35 40
y (c
m)
x (cm)
M80
L2R2
ARDEC Design vs. M80 & Contractor Design
Contractor Design
Target = A36 Mild Steel @200m, 45 deg angle
Summary
• Significant yaw growth below Mach 1• Ability to meet distance requirement dependant on
initial QE and projectile ogive cuts being free of debris
• Trajectory similar to that of the M80• Hard target penetration ability not equivalent to that
of the M80• Effective against soft targets and Automobile Glass
Stephen McFarlaneProject EngineerSmall Caliber Munitions DivisionTel#: 973-724-7326Fax#: [email protected]
BACK UP
400m Velocity (1800 ft/s)
50m Velocity (2800 ft/s)
L2R2 vs. 20% Ballistic Gelatin
Ballistic Gelatin Behind Windshield
Dynamic Stability Relation to Modal Arms Damping
i β
α
PrecessionArm
NutationArm
Stable• Both arms negative (shrinking) or neutral (not growing)
• No yaw• Limit cycle
Unstable• Nutation (fast) arm is positive, precession arm positive (growing)
• Yaw level increases• Tumbling possible
Non-linear Magnus Moment
5th order fit of Magnus moment
Narrow stability bounds
Stability of this round at Mach 0.8 at experimental spin rates is questionable at best