Even cooler? We use the Tormach PCNC 1100 as an "input device" or "coordinate measuring machine" to tell us the slope of the barrel. It's an accurate, free, and actually pretty fast way which helps easily model any sort of geometry or taper, including compound angles!
After jotting down measurements from the Tormach "CMM", we model up the barrel in SolidWorks, make a quick go of the CAM in SprutCAM, then machine the engraving on the Tormach!
A quick polish with a scotch-brite wheel followed by some "hack" gunsmith cold blue gets us to a darn nice finished product!