"The Brits used cordite a lot in their shells."
Not as a primary explosive; cordite is actually a pretty poor primary explosive.
Cordite was used extensively as a propellant. It's a double-based smokeless powder, in some ways not unlike Alliant's 2400.
Cordite's primarly composition is a combination of nitrocellulose and nitroglycerine combined with stabilizers and other compounds (including, in some formulations, vaseline).
One of the problems with some cordite compositions is that, like dynamite, it could "sweat" nitroglycerine. It's theorized by some that this led to the loss of at least one Royal Navy ship in the years prior to WW I, and it may have contributed to the losses of Queen Mary and several other British ships at the battle of Jutland.