Hi Michl,
The interpretation i have read about the term is by no means based on an endured experience like yours, but it sounded to me like making some sense as, at least, its ethimology was consensual in the different languages.
Musket, Mosquete in both Castillian and Portuguese, derives from the Italian Moschetto, giving the French Mousquet.
The name originates from Mosca (fly), which initialy designated a type of Sparrow hawk (Sparviero), later attributed to the crossbow throwing bolt then, by 'transference' to firearms, to the proppeled projectile of a (shoulder) gun.
Therefore the idea of flight, as a metaphor of speed.
However i confess that i found another interpretation, which weakens the solidity of the first one, therefore bringing down my previous presumption to a humble status of uncertainty
.
There is also an old French legend saying that he name derives from the little beard flock under the inferior lip, called mosca (mouche) typicaly used by the soldiers armed with such gun.
Eventually this beard detail is also called mosca in Portuguese.
So Michl, please consider my aproach on a digestive basis
.
'Nando