Small Caliber Engraving Force Measurements Jeff Siewert Systems Engineer Arrow Tech Associates 1233 Shelburne Rd., Suite D-8 S. Burlington, Vt. 05403 802-865-3460 x19 jsiewert@prodas.com 1

Dr. Sheldon Cytron AMSTA-AR-PC-H Sponsor Contract: DAAE30-00-M-0236 Dr. Sheldon Cytron AMSTA-AR-PC-H 973-724-3368 scytron@pica.army.mil

Background Medium Caliber Measurements Large Caliber Experimental Data 1972 GE ASD: Wolf & Cochran, 25mm Large Caliber Experimental Data 1989, 1991 “Sticker” Testing, 155mm & 203mm Small Caliber Interior Ballistic Simulations Missing: Change in Pmax as F(n) Small Change in Dia. No direct push force measurement until Feb 2003

Barrel Sections for Push Force Testing Barrel Sections & Adapters Instron Machine Push Test In Progress

Bullet Construction M80 Barnes “X” Two Structural Configurations, Lubed & Unlubed

7.62mm Barrel Configuration 1.2 FC Half Angle

7.62mm Barrel Config. (con’t) “Standard” Barrel Cross Section 7.8225mm Dia. + 0.0375 7.643mm Dia. + 0.0325 4.365mm + 0.175 0.0898mm

2.5 Deg. Forcing Cone Half Angle Mod 7.62mm Reamer Dimension Key Dimension, Inches   A: 0.4370 C: 0.474 D: 0.4570 E: 0.3460 F: 0.3440 G: 0.30850 H: (TBD, est.0.2897”) K: 2.0250 L: 1.3560 M: 0.3300 N: 0.1200 O: 0.2000 Q: 20 Degree R: 2 1/2 Degree 2.5 Deg. Forcing Cone Half Angle Fabricated from Muzzle End of Original 7.62mm Bbl

Polygonal Barrel Max Feature Depth Barrel Radius 3 4 5 6 8 9 10 Note: All Barrel Corners Have 3.9116mm Radius x 0.508mm Wide 7 x Angle (D) Torque Sidewall Angle Polygonal Barrels Attractive for Ceramic / Refractory Metals

Baseline 7.62mm Bbl Avg. Push Force Function of Bullet Construction & Lube Non-linear Behavior

Baseline 7.62mm Bbl Peak Force vs. # Where is “Steady State”????

Baseline 7.62mm Bbl Push Force Sigma Lowest s w/ Bare Bullets in Std 7.62mm Bbl Moly Lube Increased s for this barrel

M80 Projectile Resist Press vs. Travel, Lube & FC Angle Non-linear behavior Differing Engraving Mechanism Assumed Elastic in 1.2 Deg. Bbl, Plastic in 2.5 Deg. Bbl

2.5 deg FC Mod 7.62mm BBl Steeper FC Half-Angle = Lower Avg. Forces Valid for Lubed and Unlubed Bullets

2.5 deg FC, Peak Force vs. # Steeper FC Angle = Lower Variability

Radial Stiffness Effect Radial Stiffness Affects Engraving Forces Bullet Construction Affects Radial Stiffness

Relative Stiffness Effect on Resistance Pressure Multiplier on baseline engraving force prediction

Effect on P-T Resistance Pressure Change Before Peak Pressure Affects Pmax Smaller Effect than originally expected

Effect on P-T Changes to Peak Pressure within “normal” limits FC Increase: Reduced Pmax, Lube: No Effect

Observations Non-linear Engraving Behavior Reduced P-T Sensitivity F(n) of Projectile Construction F(n) of Projectile Lubrication F(n) of Forcing Cone Half Angle F(n) of Bullet: Diameter, Engraved Length Reduced P-T Sensitivity Due to Travel of Resistance wrt Pmax >15 Shots Req’d to Attain SS Engraving

Small Caliber Resistance Pressure Algorithm Where: Pr = Computed Resistance Pressure PrN = Normalized Resistance Pressure BD = Band Diameter, Calibers BL= Band Length, Calibers Mat’ FF = Material Code, 1.0 for Fe & Cu, 0.2 for Plastics Stiffness FF = Stiffness Factor from chart FC Len = Forcing Cone Length K = Small Residual Constant Q = Forcing cone angle (included angle)

Predicted vs. Calc Resistance Pressure Data Collection Length Limited by Column Buckling of Punch

Conclusions Small Caliber Engraving is a More Complex Relationship Than Expected Closed Form Equation Can Be Used For Approximations Detailed Knowledge Req’d of: Barrel: Lands & Grooves, FC angle Bullet: Construction, Lubrication More Sophisticated Barrel Geometries (Polygonal) are under study