Hi HJ,
The distinctions between fowler and musket get even more complicated when you add "fusils" to the mix. Fusil is just a French word for "gun". In the latter half of the 17th century, when flintlocks were being introduced to the French military, they formed units called "fusiliers" which were soldiers issued flintlock guns and used to guard artillery. The match lock musket was still the dominant firearm but they found that matchlock musketeers with their burning matches were dangerous around powder magazines and artillery positions. Hence, when flintlocks because available, the French quickly issued flintlock guns they called fusils to troops assigned to guard artillery and powder magazines. Fusil did not refer to bore and barrel length at that time rather that the gun was a flintlock. Later, the term fusil came to be associated with lighter and smaller caliber guns usually carried by officers and NCOs. Eventually, "carbine" and fusil came to mean just about the same thing.
dave