I want to dispel some mysteries about "flat shooting" with this thread and hopefully to elevate the knowledge of basic ballistics. I suspect the info below will be pretty simple to some, but to others "flat shooting" is a mystery.
How flat a rifle will shoot depends on two and only two variables (assuming it is functioning properly). These are:
- The ballistic coefficient (BC or sometimes C) of the bullet
- The velocity of the bullet
The ballistic coefficient is a measure of drag or how well the bullet slips through the air. The higher the BC the less horizontal velocity a bullet will lose during its flight. Therefore a higher BC bullet shoots "flatter" that is to say it covers more horizontal distance in the same time frame as a lower BC bullet (assuming equal inital velocities).
A BC of 1 is a perfect bullet, because it loses no energy to wind drag (resistance). A BC of 0 is a terrible bullet, it comes out of the barrel and just drops to the ground, it would be the case where the bullet immediately dumps all its energy to the surrounding air as heat (and itself what be quite hot even if it held together). A BC greater than 1 is impossible, that would suggest that somehow the bullet was gaining energy merely by flying. By the way, BC is earth atmosphere realitive. BC's across the boards would go up if we were having a shoot on mars or the moon. Why? Less atmosphere to contend with and incidentally that does suggest that the 270 would be a more lethal elk round at a greater distance if we were chasing bulls on the moon.
Either BC (0 or 1) is unrealistic and most coefficients are in the area of .3 or so. But it is good to understand what happens in extreme cases.
Now velocity. If two bullets of the same mass and same BC are shot at the same angle to the ground, the flatter shooting will be that which has a higher velocity. This is because all bodies fall to the earth at the same rate regardless of mass. It is one of newton's laws and galileo demonstrated it by dropping lead balls off of galloping horses. Its not intuitive but true.
So the faster bullet covers more horizontal distance with the same drop as a slower bullet. The flatness of cartridge or rifle is measured in how much drop per distance covered. If you cover that distance faster you will drop less because the time interval between markers is less.
Knowing this it is possible to see why some people say a 243 or a 270 is flatter shooting than other rifles. This is simply because these cartridges tend to push the bullets at faster rates compared to other rounds (like the 30-06 or even worse the 444 marlin). However by careful selection of bullets and mass it is possible to create a 30-06 that shoots as flat as a 270.
Well I hope some find this useful. Feel free to point out any errors or omissions.
BTW, Expatriate mentioned basically the same thing to Lever awhile back, in fewer words over a couple of posts. Here it is if you would like to read ballistics from someone elses perspective.