According to the Kuhnhausen book the original gas port size for a Model 1100 3" Magnum lead shot barrel is one orifice 0.073" which is too small for reliable function with steel shot loads. The orifice should be increased to 0.081", done in drill sized steps to minimize the possibility of breaking a drill bit off in the gas port. I made a small hex aluminum handle drilled to accept the orifice drill bits then drilled and tapped through the side to accept a set screw to hold the orifice drill bits that I had ground a small flat on the shank. I used number drills and went up consecutively turning the bits by hand only until I reached 0.081", it went really easy and didn't take too long and worked perfectly when I test fired it. In the book it also states that if your gun does not function properly with magnum steel shot loads at 0.081" you can open the port up further (also in steps) up to 0.086" maximum diameter.