text: what is the circumference of a shotgun shell?   well, the shotgun gauge bore diameter are 10 gauge  0.76" (19.7 mm)  12 gauge 0.73" (18.5 mm)  16 gauge  0.66" (16.8 mm)  20 gauge  0.62" (15.6 mm)  28 gauge 0.55" (14.0 mm)   the hull thicknesses very from manuafcturer to manufacturer, but are larger than the bore diameter. hope this helps.