RE: Slug Question
Another issue with rifled slugs is the need to be sensitive to barrel length. Todays factory rifled slug guns, as well as most aftermarket rifflled barrels tend be at least 20+in. This makes shooting rifled slugs even more detrimental to downrange trajectory.
With rifled slug design....
Once all the powder is burned and the slug reaches terminal velocity (and the rifling has imparted spin to the slug), the barrel's job is done. That happens in the first 18-20 inches of barrel - a longer barrel only slows the slug down with friction.
This means that in todays rifled slug guns, many of which are 24in length, you have an extra 6in of barrel length accomplishing nothing but slowing your bullet.