Those that said to pattern the gun and use the shell that
is best (inside 40 yds) are on it.

IMO 50 yds is a LONG shot.
Usually use 7-1/2 shot but 8 or 9 will work
I've use 6 too but like having the extra shot so only if
collared dove or pigeons are also a possibility.

Mourning dove are easy to kill compared to collards or pigeons.