He has a row of greenhouses with workers inside directly behind his target. Yes they are a long way away but if he flinches and just clips the top of the safe, the slug skips upwards and will go a long way towards the greenhouses.
If he flinches and clips the side, the slug goes off in the direction of the neighbor's house.
Wax plug, with small shot.
If it clips an edge it breaks up into tumbling pieces with no range.
If he misses all together, it has the aerodynamics of a tumbling can with no range.
There is no shot shell load of any kind that would travel half that distance.