This is one of four copper alloy powder horn lids used to prime the large bronze and iron guns of the Mary Rose. This is one example – shown twice so you can see the mechanism.
The nozzle has an internal spring-loaded cover, operated by a lever on the outside, which ensures that every time the horn is used, the same amount of powder is released. The ‘horn’ itself has been lost, but while it may have been made of horn, as the name suggests, they could also be made of ivory, leather or wood.