I've never had too much trouble shimming with Surefire's chart.

They give you that point on the chart you're suppose to be aligned at prior to torquing. I always aim for the inside of this, between it and 6 o-clock. Its almost as if the start point prior to torque should be a little more toward 6 o-clock.

Either way, its a flash hider not a space shuttle. The chart works. I wouldn't go out and buy a set of feeler gauges for it. If I had a set lying around...