Top Gear is a fun show, but they often substitute humorous proclaimations for facts. If they can do it at the expense of an American machine, they will. Jeremy Clarkson, for all his talent, probably knows as much about modern weaponary as I do about high end women's footwear.
Flaunting this ignorance in a confident and mocking tone, and putting the British above the Americans in the process, is better than drugs for him. He does the same thing when comparing cars, except that he actually knows a thing or two about cars. Here it's just absurd.
The Americans, as well as the Russians and whoever else uses sooth bore technology does so for a reason--and these reasons were mentioned already. Departing from the rifled barrel technology would not have been done on a whim. Smoothbore guns fire the sabot round, which requires no rifling--as mentioned. They also fire actively guided munitions, which can autocorrect their trajectory.
The concept of gyroscopic stabilization is in its 3rd century, and it should come as no surprise that new technologies are being implemented to improve upon it. Just because the Brits are sticking to a method that's older than the United States doesn't mean they're doing it right.
