Barrels of gunpowder

There is a note in Charles Boxer's book Tromp's Journal 1639 that barrels of gunpowder were 100 lbs. each. That would resolve a question about gunpowder after the Battle of Scheveningen, where in some cases the amounts were in barrels and in other cases they were in hundreds of pounds. Sources:

1. C.T. Atkinson, Ed., The First Dutch War, Vol.V, 1912.
2. Charles R. Boxer, The Journal of Maarten Harpertszoon Tromp Anno 1639, 1930.