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. (Note: Not compatible with the Large Brake Adapter or the V3 Rail Adapter.)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 Integral 3.5 foot sensor cordKit Includes: Display Unit Bayonet-style sensor (Bayo) Thick and thin rubber V-block spacers Heavy duty strap with thumb nut tightener Ultra-compact storage container.