Glass balls are an interesting thought Mike.
Glass balls for competition in the U.S. were mostly replaced by a variety of targets during the 1880s
https://docs.google.com/document/d/1I_5GfGqfidbrfhpwzMvsccjDxjCd39M6nERp99wVEBQ/edit

This states however that balls were manufactured into the 1920s, mostly for shooting galleries and "Wild West" shows
https://traphof.org/artifacts/history-of-glass-target-balls

Mark: are you suggesting that birds were tossed in the air from behind the barrier?
In some Columbaire shoots the shooter is standing on an elevated platform and there are markers above which the pigeon must fly to be a legal shot