MagnetoSpeed MagnetoSpeed Sporter, Chronograph, Fits Centerfire Rifles, Black/Red, Will Not Work with Suppressors MS_SPT The MagnetoSpeed Sporter chronograph was designed to be used on barrels from 1/2 inch up to 1 inch in diameter. In can also accommodate muzzle brakes and flash hiders up to 2.7 inches in length. Ideal for contoured rifle barrels (sporter barrels) and long-barreled revolvers.