1. May 2004NDIA Small Arms Las Vegas, 2004 11 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

2. May 2004NDIA Small Arms Las Vegas, 2004 2 Sponsor Contract: DAAE30-00-M-0236 Dr. Sheldon Cytron AMSTA-AR-PC-H 973-724-3368 scytron@pica.army.mil

3. May 2004NDIA Small Arms Las Vegas, 2004 3 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

4. May 2004NDIA Small Arms Las Vegas, 2004 4 Barrel Sections for Push Force Testing Instron Machine Barrel Sections & Adapters Push Test In Progress

5. May 2004NDIA Small Arms Las Vegas, 2004 5 Bullet Construction Two Structural Configurations, Lubed & Unlubed M80 Barnes “X”

6. May 2004NDIA Small Arms Las Vegas, 2004 6 7.62mm Barrel Configuration 1.2 FC Half Angle

7. May 2004NDIA Small Arms Las Vegas, 2004 7 “Standard” Barrel Cross Section 7.8225mm Dia. + 0.0375 7.643mm Dia. + 0.0325 4.365mm + 0.175 0.0898mm 7.62mm Barrel Config. (con’t)

8. May 2004NDIA Small Arms Las Vegas, 2004 8 Mod 7.62mm Reamer Fabricated from Muzzle End of Original 7.62mm Bbl Dimen sion 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

9. May 2004NDIA Small Arms Las Vegas, 2004 9 Polygonal Barrel Max Feature Depth Barrel Radius 3 4 568 910 Note: All Barrel Corners Have 3.9116mm Radius x 0.508mm Wide 7 x Angle (  ) Torque Sidewall Angle Polygonal Barrels Attractive for Ceramic / Refractory Metals

10. May 2004NDIA Small Arms Las Vegas, 2004 10 Baseline 7.62mm Bbl Avg. Push Force Function of Bullet Construction & Lube Non-linear Behavior

11. May 2004NDIA Small Arms Las Vegas, 2004 11 Baseline 7.62mm Bbl Peak Force vs. # Where is “Steady State”????

12. May 2004NDIA Small Arms Las Vegas, 2004 12 Baseline 7.62mm Bbl Push Force Sigma Lowest  w/ Bare Bullets in Std 7.62mm Bbl Moly Lube Increased  for this barrel

13. May 2004NDIA Small Arms Las Vegas, 2004 13 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

14. May 2004NDIA Small Arms Las Vegas, 2004 14 2.5 deg FC Mod 7.62mm BBl Steeper FC Half-Angle = Lower Avg. Forces Valid for Lubed and Unlubed Bullets

15. May 2004NDIA Small Arms Las Vegas, 2004 15 2.5 deg FC, Peak Force vs. # Steeper FC Angle = Lower Variability

16. May 2004NDIA Small Arms Las Vegas, 2004 16 Radial Stiffness Effect Radial Stiffness Affects Engraving Forces Bullet Construction Affects Radial Stiffness

17. May 2004NDIA Small Arms Las Vegas, 2004 17 Relative Stiffness Effect on Resistance Pressure Multiplier on baseline engraving force prediction

18. May 2004NDIA Small Arms Las Vegas, 2004 18 Effect on P-T Resistance Pressure Change Before Peak Pressure Affects Pmax Smaller Effect than originally expected

19. May 2004NDIA Small Arms Las Vegas, 2004 19 Effect on P-T Changes to Peak Pressure within “normal” limits FC Increase: Reduced Pmax, Lube: No Effect

20. May 2004NDIA Small Arms Las Vegas, 2004 20 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

21. May 2004NDIA Small Arms Las Vegas, 2004 21 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)

22. May 2004NDIA Small Arms Las Vegas, 2004 22 Predicted vs. Calc Resistance Pressure Data Collection Length Limited by Column Buckling of Punch

23. May 2004NDIA Small Arms Las Vegas, 2004 23 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