Mount & Blade: Warband

From the main menu, choose to setup a custom battle. Choose Stavros as your hero/character, make both army compositions 100% archers, set the map as Haima Castle on Siege Defense, Army Size at max and finally pick the enemy faction as Outlaws (due to no shields).

You should spawn on the castle walls and begin firing bolts into the large amount of enemies. With this setup, it took me about 5-10 bolts to get a shot with a difficulty over 6. Things that will affect the difficulty of the shot are range and placement, so if you manage to get a headshot you should achieve the desired difficulty.