Prior to Pickett's Charge why did the rebels believe the Union cannons on Cemetery Ridge were destroyed?

Answer 1

The commander of the Confederate charge, James Longstreet, was not thoroughly convinced that the Union artillery was completely silenced. In fact,generalHunt, the commander of the Union artillery, had given orders to reduce the volume of fire to conserve ammunition and to mask the placement of his many batteries of artillery.It was Hunt's plan to commence heavy fire when the Confederates moved into the open fields on either side of the Emmitsburg road. This he did with devastating effect.

Longstreet was aware that this might happen but ordered the charge under pressure from Robert E. Lee and due to the fact that he had been informed by his artillery commander, Colonel Alexander, that the Confederate artillery had nearly exhausted their own supply of ammunition.