Roaring Meg (cannon) - Wikipedia. Roaring Meg was a mortar cast in 1646 for the siege of Goodrich Castle. With a 15.5-inch (390 mm) barrel diameter and firing a 2 long cwt (220 lb; 100 kg) hollow ball filled with gunpowder, Roaring Meg was the largest mortar of the English Civil War.The weapon and its ammunition is believed to have been manufactured near Lydbrook at Howbrook furnace and forge ...