Ok gents, I thought I would briefly cover a common issue encountered when sighting in or shooting a rifle in multiple climates.
Ballistic Efficieny=ratio of pressure to velocity. Higher pressure equals higher velocity (or sometimes a big bang in your face if experimenting with your own loads!)
Many factors affect chamber pressure, but the most common one we will encounter on the battlefield and that most take for granted is temperature difference. A hot bullet in a hot gun equals increased chamber pressure and higher velocity. Same goes for shooting a gun in the afternoon that has been sighted during the cooler hours of the morning. What does this mean to the shooter? It means that you will see a rise in shot groups on hotter days, sometimes 1-2 Minutes of Angle worth. This means a raise of 1-2" at 100 yards or 4-8" at 400 yards, 8-16" at 800 yards and you start to see why it's important for accuracy. Also a good reason to not chamber a round, or cycle your bolt if you have a semi auto and you have the opportunity. With practice, a good sniper will just take this into account and hold 1 MOA down and send it.
Below is a very rudimentary example.
While a good ballistic calculator is a must have these days, it is also good to know and learn the basics of ballistics.
Hold 1 right and send it. -Brandon