In-bore balloting is defined as any transverse motion of a projectile in the gun tube. In-bore
balloting can be caused by any one or more of the following conditions:
- Projectile center of gravity (CG) and principal axis offset from the bore centerline.
- Projectiles, as manufactured, are not perfectly concentric.
- Projectile / gun tube clearances may exist at projectile surfaces.
- Insufficient stiffness of the projectile / gun tube interface will exacerbate conditions caused by minimal balloting.
- Projectile wear produces or widens gaps (clearances) between the projectile bourrelet surfaces and the gun bore.
- Gun tube curvature (including bore irregularities) exist in all gun tubes.
- Gas dynamics produce irregular pressures at the projectile base.
Some of the applications of in-bore balloting are:
- Product verification.
- Used in rapid design/build cycle; achieve first-design success.
- Investigation of projectile structural integrity.
- Predict muzzle exit condition sensitivity studies.
- Perform rapid sabot design studies for APFSDS projectiles.
- Assess production tolerance effects; use of Statistical Process Control (SPC) data.
- Predict in-bore performance and aerodynamic resonance.
- Determine influence of design parameters on dispersion.
- Assess the effect of bore curvature on mean point of impact (MPI)
The muzzle exit flash X-Ray, shown below, is of a heavy metal core for a 30mm round
that has bent as
a result of in-bore forces.
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