BANDSLIP Advancements 

by Michael Minnicino 

ARL-TR-4943 September 2009 

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Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5069 

ARL-TR-4943 September 2009 

BANDSLIP Advancements 

Michael Minnicino 

Weapons and Materials Research Directorate, ARL 

Approved for public release; distribution is unlimited.
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September 2009 

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1 August 2008–30 September 2008 

4. TITLE AND SUBTITLE 

BANDSLIP Advancements 

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6. AUTHOR(S) 

Michael Minnicino 

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H80 

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U.S. Army Research Laboratory 

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Aberdeen Proving Ground, MD 21005-5069 

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13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

A munition is said to be despun when the munition’s angular velocity is significantly less than its band’s angular velocity, thus 

the band slips on the munition and, hence, the name “slipband.” With the emergence of smart munitions that possess advanced 

guidance for dynamic targeting capabilities, despun munitions are seen as the best approach for survivability of these finstabilized, canard-guided munitions due to the reduced aerodynamic loads on the fins and canards. The BANDSLIP code used 

for predicting the spin history of munitions has been improved. The most notable improvement is the capability to simulate 

projectiles shot through progressive twist gun tubes. 

15. SUBJECT TERMS

rotating band, slip band, despun, BANDSLIP 

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OF ABSTRACT 

UU 

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18 

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Michael Minnicino 

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iii

Contents 

List of Figures iv

1. Introduction 1

2. Theory 1

3. Simulation of Projectile Spin History With Progressive Twist Rate Gun Tubes 3

4. Case Study 5

5. Summary 10

Distribution List 11 
iv

List of Figures 

Figure 1. Illustration of a typical two-piece band cross section. ....................................................2

Figure 2. Section of a gun tube showing a single rifling land to illustrate (a) the measurement 

system used to define a gun tube’s (b) rifling profile. ...............................................................4

Figure 3. M67 zone 3 filtered base-pressure time curve. ................................................................5

Figure 4. Linear acceleration time history. .....................................................................................6

Figure 5. Linear velocity and displacement time histories. ............................................................6

Figure 6. Slipband angular acceleration time history. ....................................................................7

Figure 7. Comparison of slipband and bandseat angular velocity time histories. ..........................8

Figure 8. Comparison of slipband and bandseat angular velocity time histories during the 

period of relative motion. ...........................................................................................................8

Figure 9. Comparison of experimental and BANDSLIP 2.0 predicted projectile muzzle 

angular velocities for various propelling charge masses. ..........................................................9
1

1. Introduction 

The original BANDSLIP R1.0 was developed by Sandia National Laboratory (Livermore, CA) 

as a computational tool used to predict the dynamic behavior of despun munitions.1

 BANDSLIP 

R1.0 was distributed to the U.S. Ballistics Research Laboratory in 1989 and was later 

successfully used to qualitatively predict the dynamic behavior of a 105-mm despun munition 

using different slipband designs.2 This code was incrementally modified until it was unified as 

BANDSLIP R1.2.3 A detailed explanation of the code can be found in Minnicino.3 Recent 

modifications of the BANDSLIP R1.2 code are described herein. This new version of the code 

is referred to as BANDSLIP 2.0. 

2. Theory 

A munition is said to be despun when the munition’s angular velocity is significantly less than 

the obturation band’s angular velocity, thus the band slips on the munition and, hence, the name 

“slipband.” With the emergence of smart munitions that possess advanced guidance for dynamic 

targeting capabilities, despun munitions are seen as the best approach for survivability of these 

fin-stabilized, canard-guided munitions due to the reduced aerodynamic loads on the fins and 

canards. 

The cross section of a typical slipband design is shown in figure 1. From this figure, it is seen 

that the slipband rides on a section of material denoted as the bandseat, which is outlined in the 

figure by dashed lines. From experience, it is recommended that the slipband ride on a polymer 

bandseat for performance and reliability.2

 The polymer bandseat is permanently fixed to the 

subprojectile. Therefore, the bandseat rigid body dynamics, i.e., linear and angular 

displacements, linear and angular velocities, and linear and angular accelerations, are equivalent 

to the subprojectile’s rigid body dynamics. A design utilizing a distinct bandseat material 

relative to the slipband and the subprojectile is referred to as a two-piece slipband design. 

Conversely, if the bandseat is provided by the subprojectile material, it is referred to as a onepiece slipband design. The base pressure is the pressure acting normal to the munition’s surfaces 

rear of the band due to the propellant deflagration. The tube pressure is realized after the 

slipband is radially compressed by passing through the gun’s forcing cone and subsequently

 1 Nielan, P. E. Spin Rate Prediction for Projectiles with Slipping Obturators; presentation handout, U.S. Army Ballistics 

Research Laboratory: Aberdeen Proving Ground, MD, 7 September 1988. 

2 Kaste, R. P. Development of a Design Methodology for Slipband Obturators; BRL-TR-3297; U.S. Army Ballistics 

Research Laboratory: Aberdeen Proving Ground, MD, 22 November 1991. 

3

 Minnicino, M. A. BANDSLIP R1.2 Theory and User’s Guide; ARL-TR-3598; U.S. Army Research Laboratory: Aberdeen 

Proving Ground, MD, September 2005. 
2

Figure 1. Illustration of a typical two-piece band cross section. 

remains radially confined by the gun tube’s inner wall. The effect of the tube pressure provides a 

compressive radial stress between the slipband and the bandseat. The magnitude of the induced 

radial stress is difficult to determine and is not constant along its length (x-direction) but can be 

adequately estimated through a Lamé stress analyses. 

There are two processes that decouple the projectile from the gun tube’s rifling. The first is 

melting the interface between the bandseat and slipband. The second is reducing torque transfer 

capability between the bandseat and slipband by the base pressure. These two processes are 

explained next. 

The BANDSLIP code calculates the torque required to spin the projectile at the same rate as the 

kinematically constrained slipband. The code also calculates the maximum torque that can be 

transmitted from the slipband to the bandseat/subprojectile. When the maximum transmittable 

torque is less than the required torque, the slipband “slips,” i.e., it spins relative to the bandseat. 

Heating of the bandseat-slipband interface is generated by this relative motion through frictional 

heating and is proportional to the coefficient of friction between these two surfaces and the 

difference in rotational velocity. The amount of heating is significant enough to melt either one 

or both of the bandseat or slipband materials, resulting in a liquid interface that is unable to 

transmit torque. (See Minnicino3 for a more detailed explanation of the heating analysis.) 

The base pressure acts to negate the tube pressure. Hydrostatics dictates that when the 

magnitude of the base pressure becomes larger than the effective tube pressure, the normal 

traction between the bandseat and slipband on the radial surface is 0. No torque can be 

transmitted across the radial surface when the normal traction is 0. This condition is termed 

“lift-off” as the slipband is lifted from the bandseat by the base pressure. The axial surface 

becomes the only surface able to transfer torque from the slipband to the bandseat under this 

condition. Additionally, it should be noted that the slipband still provides obturation since there 

x

centerline Projectile 

Nose

Projectile 

Base

r

Base 

Pressure

Tube 

Pressure

subprojectile

bandseat

slipband

axial surface 

area

radial surface 

area
3

is still a gas-tight seal at the bandseat-slipband axial surface interface. The munition’s angular 

velocity is therefore limited to its angular velocity when axial and radial surfaces have melted or 

the radial surface has lifted and the axial surface has melted. 

3. Simulation of Projectile Spin History With Progressive Twist Rate Gun 

Tubes 

A general formulation of the slipband’s dynamic quantities is now developed. Recall that the 

slipband’s linear dynamic quantities are equivalent to the bandseat/projectile and its angular 

dynamic quantities are kinematically constrained by the rifling. A gun tube’s rifling profile is 

expressed in terms of circumscribed arc length of the lands and grooves in a plane normal to the 

tube’s centerline, as shown in figure 2a. The result of this rifling profile representation for a 

constant twist gun tube is a straight line, as shown in figure 2b, where the x-s coordinate system 

is 0 at the origin of rifling and twist is defined as the revolutions per caliber of travel. Certain 

guns, such as the M119, have a progressive or gain-twist rifling profile where the twist at the 

origin of rifling is less than the twist at the muzzle. Further, the rifling profile need not be linear. 

For example, the rifling profile for the M119 gun tube is quadratic and can be expressed 

generally as follows: 

2

1 23 s x cx cx c () .   (1) 

However, the arc length is equivalently 

s  r . (2) 

Defining the gun rifling as a function of the independent spatial variable, x, in equation 1 and 

using the arc length-rotation relation given in equation 2 allow simple differentiation of the 

rotational velocity and acceleration as follows: 

( ) , s x

r

  (3) 

1 ,

. . d s(x) ds θ x

dt r r dx

        (4) 

and 

2 . .. . .. 2

2

11 1 () , d ds d s ds

x x x

dt r dx r dx r dx

         (5) 
4

Figure 2. Section of a gun tube showing a single rifling land to illustrate (a) the 

measurement system used to define a gun tube’s (b) rifling profile. 

where s(x) is the prescribed rifling profile, .x is the projectile’s linear velocity, ..x is the projectile 

linear acceleration, and r is the tube radius. Applying Newton’s second law gives 

..

, PAx

m  (6) 

where P is the base pressure, A is area the base pressure acts on, and m is the projectile mass. 

Once the linear acceleration is computed for the current time step, the linear velocity and 

displacement are calculated using finite-difference methods. Subsequently, the angular 

acceleration for the current time step is computed using equation 3. The slipband’s angular 

velocity and displacement are calculated using finite-difference methods. However, the 

bandseat’s/projectile’s angular quantities are determined by a more complicated algorithm 

discussed in Minnicino.3

 

(a) (b) 

s 

x 

s = Arc Length 

Arc measurement 

plane orthogonal to 

tube centerline 

x = Axial Measurement 

Location 

Origin of Rifling 

Rifling Land 
5

4. Case Study 

In this section, the BANDSLIP software is a-posteriori compared with the 105-mm artillery very 

affordable precision projectile (VAPP) slipband demonstration data. The VAPP uses a twopiece slipband design and is shot through an M119 gun, which uses a progressive twist gun tube. 

The input to the BANDSLIP software includes the two-piece band geometry and material 

properties, the projectile’s inertial properties, and a filtered base pressure-time history. 

Additionally, the compressive radial prestress between the slipband and bandseat is estimated to 

be 9.43 ksi (65 MPa) through a Lamé analysis. The coefficient of friction between the slipband 

and the bandseat is assumed to be 0.10. 

To illustrate the utility of the BANDSLIP software and provide evidence that the updated code 

correctly accounts for progressive twist gun, the results for an M67 zone 3 VAPP shot are 

presented. A filtered base pressure-time history for an M67 zone 3 VAPP shot is used, as shown 

in figure 3. The linear acceleration, shown in figure 4, is simply the base-pressure time history 

linearly scaled per equation 6. It should be noted that the linear dynamic quantities are the same 

for the slipband and the bandseat/projectile since they are physically constrained. The 

BANDSLIP computed linear velocity and displacement time histories are shown in figure 5. 

The experimental muzzle velocity for this shot is 231 m/s, and the travel distance for the M119 is 

2.70 m. BANDSLIP predicts the muzzle velocity as 230 m/s, and the travel distance is 2.68 m. 

Figure 3. M67 zone 3 filtered base-pressure time curve. 
6

Figure 4. Linear acceleration time history. 

Figure 5. Linear velocity and displacement time histories.
7

The angular acceleration of the slipband is shown in figure 6. Compared to a constant twist rate 

gun tube, the angular acceleration does not decay in the same manner as the linear acceleration. 

However, since VAPP is shot through a progressive twist gun tube, the angular acceleration 

remains large, even as the linear acceleration significantly decreases. 

Figure 6. Slipband angular acceleration time history. 

The angular velocity of the slipband and the bandseat is shown in figure 7. The bandseat’s 

angular velocity is the same as the slipband’s angular velocity until slipping begins. At that time, 

the bandseat’s angular velocity increases at a slower rate than the slipband. Figure 8 highlights 

the data from 8 to 11 ms in figure 7. In this figure, the angular velocities of the bandseat are less 

than the slipband beginning at ~8.5 ms. The rate of divergence in angular velocity is small near 

this time. The slip is from the torque’s capability of being transferred from the slipband to the 

bandseat; projectile assembly is less than required. At 9.75 ms, the rate of divergence increases 

significantly because the slipband lifts from the bandseat by the base pressure. Recall that a 

compressive radial prestress of 9.43 ksi (65 MPa) is prescribed between the slipband and 

bandseat; the base pressure at 9.75 ms is ~9.43 ksi (65 MPa). Therefore, once the compressive 

radial prestress has been overcome, only the axial interface can transmit torque and at a much 

lesser extent. The large difference in angular velocities produces more frictional heating that, if 

given enough time, can cause the axial face to melt and thereby cease the torque transmission. 

At the moment when torque can no longer be transferred, the bandseat/projectile’s angular 

velocity obtains its final value, as represented by the flat slope of the bandseat’s angular velocity.
8

Figure 7. Comparison of slipband and bandseat angular velocity time histories. 

Figure 8. Comparison of slipband and bandseat angular velocity time histories during the period 

of relative motion.

Slipband “lift-off”

Slip Starts

Axial Face Melts 
9

A comparison between the experimental and BANDSLIP-predicted projectile angular velocities 

at muzzle exit is shown in figure 9. It is seen that for low propelling charge masses, BANDSLIP 

overpredicts the muzzle angular velocity. Conversely, it is seen that BANDSLIP underpredicts 

the angular velocity at larger propelling charge masses. BANDSLIP provides insight into twopiece band designs but not quantifiable numbers. 

Figure 9. Comparison of experimental and BANDSLIP 2.0 predicted projectile muzzle angular 

velocities for various propelling charge masses. 

The lack of quantitative results can be attributed to uncertainties of interface stress and 

coefficient of friction between the slipband and bandseat materials. The slipband material is 

nylon. Depending on formulation and manufacturing process, the thermomechanical material 

properties of nylon vary immensely. Typical commercial-grade values were chosen for the 

BANDSLIP analysis. Additionally, viscoelastic effects of the slipband and bandseat materials 

were not considered in the BANDSLIP software, therefore, possibly adding to lack of 

quantitative results. 
10

5. Summary 

BANDSLIP R1.2 has successfully been updated and can simulate despun projectiles shot 

through progressive twist rate gun tubes. This updated version of the code is denoted as 

BANDSLIP R2.0. The method in which rifling profiles are defined is explained. Lastly, the 

derivation of the equations used to simulate progressive twist rate gun tubes using a general 

rifling profile has been documented. 

BANDSLIP predictions may be improved by more comprehensive testing of the slipband and 

bandseat materials in order to accurately determine their thermomechanical elastic properties and 

significance of viscous effects. Additionally, the thermomechanical material properties can be 

used in a three-dimensional, finite-element analysis to provide a more detailed interface stress 

between the slipband and bandseat as they pass through the forcing cone and engrave on the 

rifling. 
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