FD

Rotating bands

Dirt and burns cause improper sitting of the round

Tube conditioning

A cold tube offers greater resistance to projectile movement than a warm tube

Propellant residues

Burned propellant and chemical agents leave residues on the bore surface

Moisture content of propellant

Charges come in sealed aluminium foil, only remove it from the seal just before firing

Position of charges in chamber

Charges need to be flushed against the obturator spindle

Non-uniform ramming

Creates a non-airtight chamber, resulting in escaping gasses and a smaller propellant chamber

Coppering

Deposit of a thin film of copper on the bore, resulting from friction that removes the outer surface of the band

Velocity Trends

Same lots of round with diff. MV

Ammo Lots

Mass production with diff. raw materials and machines

Weight of projectile

Projectiles have different weights, WP rounds tend to be heavier than HE

Propellant temperature

Proper storage of charges to ensure uniform prop. temp. The thermal seal of the container protects it, thus only remove when firing.

Tolerances in new weapons

Vary in parameters (size of powder chamber, interior dimensions of the bore to machine tolerances) during manufacture

Wear of tube

Wear and tear of bore due to hot gasses, chemical action and movement of projectile