
ACTIVE: Graves fires an explosive shell in a straight line, dealing heavy physical damage to the first champion it hits (also damages non-champion enemies whilst in flight). After hitting a champion or reaching the end of its range, the shell explodes dealing physical damage in a cone behind the target.
An interesting idea, but I'm hesitant to say it'd work without knowing more about how hitboxes are done in League. The angles and 'safe zone' will change depending on distance from the epicenter, 'shielding object' hitbox size and overall visibility if it works similar to Zigg's ult.
Now you're earlier suggestion of a 360 degree Ashe volley (multiple linear skillshot arranged in a circle) would be much easier to program, and combined with a very clear marker on the epicenter (like a mine/obelisk/tower or something) it may be a very interesting addition and I don't see too many problems with it.
What would you like to see happen if say, someone was standing directly on the epicenter?