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Advanced Small Caliber Engraving Force Measurements

Explore small caliber interior ballistic simulations and force testing methods for improved accuracy. Learn about the intricate relationship between bullet construction, lubrication, and engraving mechanisms in barrel sections.

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Advanced Small Caliber Engraving Force Measurements

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  1. Small CaliberEngraving ForceMeasurementsJeff SiewertSystems EngineerArrow Tech Associates1233 Shelburne Rd., Suite D-8S. Burlington, Vt. 05403802-865-3460 x19jsiewert@prodas.com 1

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

  3. 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 Pmax as F(n) Small Change in Dia. No direct push force measurement until Feb 2003 Background

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

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

  6. 7.62mm Barrel Configuration 1.2 FC Half Angle

  7. 7.62mm Barrel Config. (con’t) 7.8225mm Dia.+ 0.0375 7.643mm Dia.+ 0.0325 4.365mm+ 0.175 0.0898mm “Standard” Barrel Cross Section

  8. Fabricated from Muzzle End of Original 7.62mm Bbl 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 Mod 7.62mm Reamer 2.5 Deg. Forcing ConeHalf Angle

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

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

  11. Where is “Steady State”???? Baseline 7.62mm BblPeak Force vs. #

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

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

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

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

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

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

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

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

  20. 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 Pmax >15 Shots Req’d to Attain SS Engraving Observations

  21. 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)

  22. Predicted vs. CalcResistance Pressure Data Collection Length Limited by Column Buckling of Punch

  23. 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 Conclusions

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