Hi,
You can use either wad cutters or round heads, depending how you want to score the shot, the wad cutter will leave a clear imprint if you wish to score the outer edge of the pellet, but most bell target leagues score the Pip, a small speck of paint that is trapped when the round head pellet hits the plate, i.e. the pip has to be inside the hole or inside the scoring line to be scored up.
The shot on the left of the hole, scoring the outer edge of the pellet would be a 5, scoring the Pip it would be a 4.
Jim