In Kiley's "Artillery of the Napoleonic Wars" he mentions that at the battle of Friedland, during Senarmont's assault on the Russian center, in no longer than 30 minutes his artillery corps of 30 guns expended 2600 roundshot and 400 cannister. Were the cannons double-shotted? Or was each gun firing every 18 seconds? Would each gun have brought along a caisson during the assault?