When you get a few extra bucks look at the MagnetoSpeed chronograph it doesn't use optical screens, rather it uses a magnetic pickup similar to an electric guitar pickup. It works best with rifles and shotguns and some pistols and revolvers. The sensitivity can be programmed for small lightweight bullets that escape detection on the optical models (.204 24 grain Hornady NTX @ 3900+fps). It is not sensitive to muzzle blast, mainly because it is barrel mounted in the blast zone. Mine works with all cartridges including .22-250, 243 WSSM, 6.5x284 and even those with muzzle brakes. I only tout it because it made my life so much easier, just mount and dismount it while standing at the bench in less than 2 minutes. My two Oehler chronographs now sit unused.