A fowling piece is a flintlock with an extra-long barrel which is usually elaborately decorated and formed. It has a robust mechanism and excellent aim and as its name indicates, is used to hunt birds and small game. A fowling piece may also have two barrels. As rifling does not exist, a fowling piece likely lacks it.
The gun's name is a reference to the shotgun, which was historically known as a fowling piece, but differs by having a long barrel. The shotgun parallel is further reinforced by a fowling piece being either single or double barreled. Nectarius' version is suggestive of a sawn-off shotgun.