1. Small Caliber Engraving Force Measurements Jeff Siewert Systems Engineer Arrow Tech Associates 1233 Shelburne Rd., Suite D-8 S. Burlington, Vt x19 1

2. Dr. Sheldon Cytron AMSTA-AR-PC-H
Sponsor
Contract: DAAE30-00-M-0236
Dr. Sheldon Cytron AMSTA-AR-PC-H

3. 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

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

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

6. 7.62mm Barrel Configuration
1.2 FC Half Angle

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

8. 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: H:
(TBD, est ”) 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

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

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

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

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

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

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

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

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

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

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

20. 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

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

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