More on shells.
Michael Barry.
"The 'Helga' fired 24 rounds from its 12-pounder deck gun. These were high-explosive shells, i.e. which explode on impact. One account tells that the first shell hit the bridge.

At the same time, British Army gunners had moved an 18-pounder field gun from Trinity College. They set up by the south quays by Butt Bridge at Tara Street, and proceeded to shell Liberty Hall as well. They (army gunners)had only shrapnel shells. These did not contain high explosive and would have the effect of a glorified but high-velocity cannon-ball."

http://www.theirishstory.com/2016/03/24/the-helga-and-the-shelling-of-liberty-hall/#.VxthtfkrKt-

Author and historian Michael B. Barry studied in Trinity College, Dublin.
Michael has written several books including 'Victorian Dublin Revealed' and 'The Green Divide, an Illustrated History of the Irish Civil War'. His recent book 'Courage Boys, We are Winning, an Illustrated History of the 1916 Rising' is a best seller. It has been described in the press as the best illustrated book on the 1916 Rising, and has gone into reprint.