Flynn also adds that it was the “coolest weapon,” he’ll probably get to interact with, which could put a big question mark on Bronn’s fate following that dramatic ending.
Jerome Flynn tells Making Game Of Thrones that Qyburn’s weapon is an actual weapon that was constructed by armorers who work for the series.
While the dragon was fake, the weapon used to shoot it was very real.
As it was an actual weapon, Flynn had to undergo training for it in order to do the sequence on screen, and yes, actually shoot an arrow from it.