Fort Nelson, in Portsdown Hill Road, will fire off the north mortar battery on Sunday, April 28.
The weapon will be firing at 11am, 11.30am, 2pm, 2.30pm, 3pm and 3.30pm.
A 13-inch mortar, the weapon was the heaviest of its kind for counter-siege operations.
It was built in 1810 and could fire a missile more than 1.5 miles.
These firings will come as part of an event giving visitors the chance to get up close and personal with the artillery guns, with uniformed detachments on hand to answer questions about them.
Entry to the museum is free but some activities carry a small charge.
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