The answer for your question is on this video. Starts at 6:00 min. [ame="http://www.youtube.com/watch?v=7HjnXfZfD60"]ZBrush Tutorial (Architectural Techniques) - part 6 - YouTube[/ame]
I use Max 6 because the tools for my current expansion pack project are written for Max 6 and the tool programmers have moved onto support other projects.
I'd really recommend bumping the barrel up to 8-sided from its current 6; the extra 6 triangles will really improve the 'roundness' of the barrel at a very small cost.