Hirondelle. Not pigeons. Swallows. They refer to grades in Charlin guns, as do the running bunnies. But, from what I can tell, graded Charlins were always built to order, and the engraving could be up or down grade.
I have a copy of a page listing the Charlin grades, somewhere in the cloud, and Ill see if I can find it. But, that information on Charlins is less useful than on Darne guns, where the grading was more structured.

Best,
Ted