The MagnetoSpeed Sporter chronograph kit was designed to be used on barrels from 1/2 inch up to 1 inch in diameter. In can also accommodate muzzle brakes, flash hiders, etc, up to 2.7 inches in length. Ideal for contoured rifle barrels (sporter barrels). MagnetoSpeed Sporter features: Simple, one-button cycling display (shows recent shot velocity and statistics, plug in to turn on) Battery : 9-Volt (included) Easy access battery compartment, no need for screwdriver to swap batteries Three sensitivity settings for fine-tuning Integral, quick-attach strapping system; with metal buckle and triad thumb nut Proven technology with updated sensor design Mfg: Magnetospeed