MagnetoSpeed V3, Chronograph, Fits .5 - 2 Diameter Barrels, Black/Red MS_V3_HC The MagnetoSpeed V3 ballistic chronograph kit was designed to be used on barrels and suppressors from 1/2 inch all the way up to 2 inches in diameter. In addition to the larger diameter tolerance" the V3 also has one inch more clearance in the blast zone to account for longer (up to 3" in most cases) muzzle brakes" flash hiders" etc.