Bryan Litz is a ballistician for Berger Bullets and Applied Ballistics. Bryan has authored a number of authoritative books on the subject of ballistics. His software, published by Applied Ballistics, can be found on a number of devices including the Kestrel Wind Meters by Nielsen Kellerman. The Applied Ballistics software and smart device app is considered an industry standard used by law enforcement and military units across the world.
Understanding your rifle’s and ammunition muzzle velocity is the most important parameter needed in calculating a firing solution. Establishing accurate muzzle velocity data requires the use of an accurate chronograph. The chronograph should be able to record several strings of ten shots each and calculate the string’s average muzzle velocity and one standard deviation.
What does one standard deviation mean? It means a shooter can expect that 68% of all shots fired will have a muzzle velocity falling within a band that is 10 fps above the average muzzle velocity or 10 fps below the average. The smaller the standard deviation the closer 68% of shots fired will be to the Avg. MV.
These instruments are not inexpensive so most professional grade ballistics applications have a truing function. Truing means determining the muzzle velocity by determining the amount of elevation needed to hit the target center at any range but preferably at the longest range where the projectile is still supersonic. By knowing the precise elevation needed, you can determine average muzzle velocity. I recommend that you true to using three ranges at a minimum. Also keep in mind that muzzle velocity varies with temperature, station pressure and relative humidity so run your truing calculations and several temperatures for best results. It’s a time consuming process but essential for accurate velocity data.