You do need to rule out temp affecting the rifle's velocity first.
There is still the possibility of mechanical distortion due to temperature but I and others have seen shifting at different temps to varying degrees but following a trend. For example we've seen shots drop low in winter but drop less when it's been colder but snap sharp fresh and clear than the drop seen where its been a bit warmer but very damp and horrible.
There's nothing to say it can't be a mixture but the drops we are seeing are more than ballistic calculators suggest we should see with any speed variation we see.
It is now getting to the point where I reckon I can dial it in but I need a few more shoots. And of course I may take a sample before shooting but I'm not about to start using one on a course. This is just an experiment to see what could be happening.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep