Difference between Rifled and Smoothbore?

The_Chieftain: There is an additional advantage to the rifle that people have not mentioned. Payload.   Compare the HE component of a 120mm or 125mm smoothbore HE round (or smoke component of a smoke round, etc) with that of a rifled round. Rifled 'payload' rounds tend to be noticably larger, since they don't need to devote some of their length to fins. Tuccy over on the EU forum did some searching for me, and the 120mm smoothbore HE filler is about the same as that of the 105mm rifle.