a hot shot furnace was typically a free-standing brick structure with special iron racks and grates, varying in size according to the number of round shot they were to heat and the number of cannon they served – a large furnace might hold 60 or more round shot. they were commonly wide, and anything from in length. a brick chimney was situated at one end with a firebox located in the front or side of the opposite end. the interior of the furnace was lined with fire brick and had sloping iron rails sized to hold round shot. cold round shots were placed in the furnace and allowed to roll down the inclined rails in rows. the first shots halted over the firebox at the low end and were heated "cherry red", approximately between . when they were removed, the next shots rolled down to take their place and be similarly heated. care had to be taken not to overheat the shot, as any that were hotter than "cherry red" were likely to become misshapen, and jam in the bore of the gun.