Service from London St Pancras to Paris Gare du Nord was delayed for about an hour after hitting the animal in the Haute Picardie region.
Long delays followed the tragic incident which took place about 30 miles south-east of Calais and involved a Paris-bound train.
Food and water were distributed to passengers on the Paris to London stranded at the Calais-Frethun station in northern France.
The Gare du Nord was plunged into chaos after the ammunition, apparently dating from WWI or WWII, was found in a man's backpack.
Passengers on the service from St Pancras International will be able to reach the French Mediterranean port city in just over six hours.
Businessman, who is banned by the French courts from leaving France, may also have tried to take flight to Middle East before Christmas.