ht tp://www.pilkguns.com/Chrony.shtml
CHRONOGRAPH RESULTS, ERRORS and VARIABLES
1. Temperature, altitude, & the effects these have on different powders. – As a general rule, in cold weather powders burn more slowly and will produce lower velocities than they will at higher temperatures. Loads developed which are near maximum velocity during cold weather may produce dangerously high pressures and be unsafe during hot weather.
2. Temperature of the barrel and the ammunition itself. a cold barrel will produce different results from a very hot one. The same with the ammunition.
3. Different altitudes may also affect velocity. This is also true with flying, velocities can vary for up to three days after air travel.
4. Battery – A good power supply is needed, usually a fresh alkaline battery. Low voltage will give poor or no results. Alkaline batteries hold the voltage better the carbon batteries.
5. Lighting - MUST be balanced on both sensors. If the sun changes position, you must maintain a balanced condition on both sensors. Whether in bright sunlight (using the top screens) or on shady days (in which the top screen is optional), it is critical to maintain a balanced situation on both sensors. In bright conditions do not allow direct sunlight onto the sensors.
6. Muzzle blast - If the muzzle blast reaches the first sensor before the projectile, your results will be bad or not at all. If the muzzle blast causes your screens to shake, the readings can be bad.
7. Spacing. Make sure that your sensors are properly positioned, secure and the distances are correct. If they are off by even 1/16" it will cause incorrect readings.
8. Glints - If there is water, sand, shiny metal or bright concrete on the ground below your tripod / chronograph set-up, the sunlight will bounce (reflect) off the surface shining back up on the projectile preventing the sensors from detecting a light drop (shadow) and thus result in a poor or no reading situation. Even paint the screen stand matt black to stop reflection.
9. Indoor - Fluorescent lighting is the kiss of death to any chronograph system. Their light does not allow the sensors to "see" the bullet. For indoor and low light conditions use either a light box with diffused incandescent lighting or the newer infra red light system.
10. Other variables - Depending on the quality of the chronograph & sensors, other variables such as mobile phone transmissions and high tension poles or electrified fencing can all have effects on chronograph performance. Even high static discharges from thunder storms in the area of use can result in problems.
