Small Caliber Engraving Force Measurements Jeff Siewert Systems

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 x 19 jsiewert@prodas. com May 2004 10/16/2021 NDIA Small Arms Las Vegas, 2004 1

Sponsor Contract: DAAE 30 -00 -M-0236 Dr. Sheldon Cytron AMSTA-AR-PC-H 973 -724 -3368 scytron@pica. army. mil May 2004 NDIA Small Arms Las Vegas, 2004 2

Background • Medium Caliber Measurements – 1972 GE ASD: Wolf & Cochran, 25 mm • Large Caliber Experimental Data – 1989, 1991 “Sticker” Testing, 155 mm & 203 mm • Small Caliber Interior Ballistic Simulations – Missing: Change in Pmax as F(n) Small Change in Dia. – No direct push force measurement until Feb 2003 May 2004 NDIA Small Arms Las Vegas, 2004 3

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

Bullet Construction M 80 Barnes “X” • Two Structural Configurations, Lubed & Unlubed May 2004 NDIA Small Arms Las Vegas, 2004 5

7. 62 mm Barrel Configuration 1. 2 FC Half Angle May 2004 NDIA Small Arms Las Vegas, 2004 6

7. 62 mm Barrel Config. (con’t) 7. 8225 mm Dia. + 0. 0375 7. 643 mm Dia. + 0. 0325 4. 365 mm + 0. 175 “Standard” Barrel Cross Section 0. 0898 mm May 2004 NDIA Small Arms Las Vegas, 2004 7

Mod 7. 62 mm Reamer 2. 5 Deg. Forcing Cone Half Angle Dimen sion Key A: C: D: E: F: G: H: K: L: M: N: O: Q: R: Dimension, Inches 0. 4370 0. 474 0. 4570 0. 3460 0. 3440 0. 30850 (TBD, est. 0. 2897”) 2. 0250 1. 3560 0. 3300 0. 1200 0. 2000 20 Degree 2 1/2 Degree • Fabricated from Muzzle End of Original 7. 62 mm Bbl May 2004 NDIA Small Arms Las Vegas, 2004 8

Polygonal Barrel 3 4 5 6 7 8 Max Feature Depth 9 10 Barrel Radius Torque Sidewall Angle (D) Angle x Note: All Barrel Corners Have 3. 9116 mm Radius x 0. 508 mm Wide Polygonal Barrels Attractive for Ceramic / Refractory Metals May 2004 NDIA Small Arms Las Vegas, 2004 9

Baseline 7. 62 mm Bbl Avg. Push Force • Function of Bullet Construction & Lube • Non-linear Behavior May 2004 NDIA Small Arms Las Vegas, 2004 10

Baseline 7. 62 mm Bbl Peak Force vs. # • Where is “Steady State”? ? May 2004 NDIA Small Arms Las Vegas, 2004 11

Baseline 7. 62 mm Bbl Push Force Sigma • Lowest s w/ Bare Bullets in Std 7. 62 mm Bbl • Moly Lube Increased s for this barrel May 2004 NDIA Small Arms Las Vegas, 2004 12

M 80 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 2004 NDIA Small Arms Las Vegas, 2004 13

2. 5 deg FC Mod 7. 62 mm BBl • Steeper FC Half-Angle = Lower Avg. Forces • Valid for Lubed and Unlubed Bullets May 2004 NDIA Small Arms Las Vegas, 2004 14

2. 5 deg FC, Peak Force vs. # • Steeper FC Angle = Lower Variability May 2004 NDIA Small Arms Las Vegas, 2004 15

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

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

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

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

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 Pmax • >15 Shots Req’d to Attain SS Engraving May 2004 NDIA Small Arms Las Vegas, 2004 20

Small Caliber Resistance Pressure Algorithm Where: Pr = Computed Resistance Pressure Pr. N = 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) May 2004 NDIA Small Arms Las Vegas, 2004 21

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

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 May 2004 NDIA Small Arms Las Vegas, 2004 23