Pete,
from my experience I'd suggest you to look at Ballistic Products Dangerous Game slugs. THis slug is very well known as Guallandi slug here. These kind of slug is for both smooth and rifled barrels and usualy shows very good accuracy.
The pic of slug on top is common cup-slug for use in small gauge rifles and smooth bore guns <20G. I used them in 32G. I played a lot with them, but this type of reloading, when you put slug into wad-cup is not good at all, slug deformes before it leaves barrel and do not show good accuracy.
