The main magazine held 1,000 barrels or 45 tonnes of gun powder which was stored in barrels similar to those on display. The fittings on the barrels were made of copper to prevent sparks.

Huge Cavity walls with tunnels and a wooden suspended floor with air vents prevented the build up of damp.

The lobby at the front of this magazine allowed for the manoeuvring of barrels and for changing into woollen magazine clothing.