Alvaro,
I have seen different results from day to day when chronographing the same load with several different chronographs. This can be due to several factors, but usually not the chronograph as much as temperature. Many powders are affected to some degree by warmer or cooler conditions.
But variations can also be due to the usual practice of most handloaders, who chronograph 3 or (at most) 5 shots of a certain load. As I've mentioned in other places, the ammo factories I've visited usually chronograph several dozen rounds of the same load before coming to any conclusions about velocity and consistency--and they're working indoors, in far more controlled conditions than most handloaders.
What sort of variations are you seeing from day to day?
