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

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

1


Sponsor l.jpg

Sponsor

Contract: DAAE30-00-M-0236

Dr. Sheldon CytronAMSTA-AR-PC-H

973-724-3368

scytron@pica.army.mil


Background l.jpg

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


Barrel sections for push force testing l.jpg

Barrel Sections for Push Force Testing

Barrel Sections& Adapters

Instron Machine

Push Test In Progress


Bullet construction l.jpg

Two Structural Configurations, Lubed & Unlubed

Bullet Construction

M80

Barnes “X”


7 62mm barrel configuration l.jpg

7.62mm Barrel Configuration

1.2 FC Half Angle


7 62mm barrel config con t l.jpg

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


Mod 7 62mm reamer l.jpg

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


Polygonal barrel l.jpg

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


Baseline 7 62mm bbl avg push force l.jpg

Function of Bullet Construction & Lube

Non-linear Behavior

Baseline 7.62mm Bbl Avg. Push Force


Baseline 7 62mm bbl peak force vs l.jpg

Where is “Steady State”????

Baseline 7.62mm BblPeak Force vs. #


Baseline 7 62mm bbl push force sigma l.jpg

Lowest s w/ Bare Bullets in Std 7.62mm Bbl

Moly Lube Increased s for this barrel

Baseline 7.62mm BblPush Force Sigma


M80 projectile resist press vs travel lube fc angle l.jpg

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


2 5 deg fc mod 7 62mm bbl l.jpg

Steeper FC Half-Angle = Lower Avg. Forces

Valid for Lubed and Unlubed Bullets

2.5 deg FC Mod 7.62mm BBl


2 5 deg fc peak force vs l.jpg

Steeper FC Angle = Lower Variability

2.5 deg FC, Peak Force vs. #


Radial stiffness effect l.jpg

Radial Stiffness Affects Engraving Forces

Bullet Construction Affects Radial Stiffness

Radial Stiffness Effect


Relative stiffness effect on resistance pressure l.jpg

Relative Stiffness Effect on Resistance Pressure

Multiplier on baseline engraving force prediction


Effect on p t l.jpg

Resistance Pressure Change Before Peak Pressure Affects Pmax

Smaller Effect than originally expected

Effect on P-T


Effect on p t19 l.jpg

Changes to Peak Pressure within “normal” limits

FC Increase: Reduced Pmax, Lube: No Effect

Effect on P-T


Observations l.jpg

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


Small caliber resistance pressure algorithm l.jpg

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)


Predicted vs calc resistance pressure l.jpg

Predicted vs. CalcResistance Pressure

Data Collection Length Limited by Column Buckling of Punch


Conclusions l.jpg

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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