May 2004NDIA Small Arms Las Vegas, Small Caliber Engraving Force Measurements Jeff Siewert Systems Engineer Arrow Tech Associates 1233 Shelburne Rd., Suite D-8 S. Burlington, Vt x19

May 2004NDIA Small Arms Las Vegas, Sponsor Contract: DAAE30-00-M-0236 Dr. Sheldon Cytron AMSTA-AR-PC-H

May 2004NDIA Small Arms Las Vegas, Background Medium Caliber Measurements –1972 GE ASD: Wolf & Cochran, 25mm Large Caliber Experimental Data –1989, 1991 “Sticker” Testing, 155mm & 203mm Small Caliber Interior Ballistic Simulations –Missing: Change in P max as F(n) Small Change in Dia. –No direct push force measurement until Feb 2003

May 2004NDIA Small Arms Las Vegas, Barrel Sections for Push Force Testing Instron Machine Barrel Sections & Adapters Push Test In Progress

May 2004NDIA Small Arms Las Vegas, Bullet Construction Two Structural Configurations, Lubed & Unlubed M80 Barnes “X”

May 2004NDIA Small Arms Las Vegas, mm Barrel Configuration 1.2 FC Half Angle

May 2004NDIA Small Arms Las Vegas, “Standard” Barrel Cross Section mm Dia mm Dia mm mm 7.62mm Barrel Config. (con’t)

May 2004NDIA Small Arms Las Vegas, Mod 7.62mm Reamer Fabricated from Muzzle End of Original 7.62mm Bbl Dimen sion Key Dimension, Inches A: C:0.474 D: E: F: G: H:(TBD, est ”) K: L: M: N: O: Q:20 Degree R:2 1/2 Degree 2.5 Deg. Forcing Cone Half Angle

May 2004NDIA Small Arms Las Vegas, Polygonal Barrel Max Feature Depth Barrel Radius Note: All Barrel Corners Have mm Radius x 0.508mm Wide 7 x Angle (  ) Torque Sidewall Angle Polygonal Barrels Attractive for Ceramic / Refractory Metals

May 2004NDIA Small Arms Las Vegas, Baseline 7.62mm Bbl Avg. Push Force Function of Bullet Construction & Lube Non-linear Behavior

May 2004NDIA Small Arms Las Vegas, Baseline 7.62mm Bbl Peak Force vs. # Where is “Steady State”????

May 2004NDIA Small Arms Las Vegas, Baseline 7.62mm Bbl Push Force Sigma Lowest  w/ Bare Bullets in Std 7.62mm Bbl Moly Lube Increased  for this barrel

May 2004NDIA Small Arms Las Vegas, 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

May 2004NDIA Small Arms Las Vegas, deg FC Mod 7.62mm BBl Steeper FC Half-Angle = Lower Avg. Forces Valid for Lubed and Unlubed Bullets

May 2004NDIA Small Arms Las Vegas, deg FC, Peak Force vs. # Steeper FC Angle = Lower Variability

May 2004NDIA Small Arms Las Vegas, Radial Stiffness Effect Radial Stiffness Affects Engraving Forces Bullet Construction Affects Radial Stiffness

May 2004NDIA Small Arms Las Vegas, Relative Stiffness Effect on Resistance Pressure Multiplier on baseline engraving force prediction

May 2004NDIA Small Arms Las Vegas, Effect on P-T Resistance Pressure Change Before Peak Pressure Affects Pmax Smaller Effect than originally expected

May 2004NDIA Small Arms Las Vegas, Effect on P-T Changes to Peak Pressure within “normal” limits FC Increase: Reduced Pmax, Lube: No Effect

May 2004NDIA Small Arms Las Vegas, Observations Non-linear Engraving Behavior –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 P max >15 Shots Req’d to Attain SS Engraving

May 2004NDIA Small Arms Las Vegas, Small Caliber Resistance Pressure Algorithm Where: P r = Computed Resistance Pressure P rN = 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  = Forcing cone angle (included angle)

May 2004NDIA Small Arms Las Vegas, Predicted vs. Calc Resistance Pressure Data Collection Length Limited by Column Buckling of Punch

May 2004NDIA Small Arms Las Vegas, 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