MOA or minute of angle translates to 1 inch at 100 yards, 2 inches at 200 yards etc... It's not exactly 1 inch per 100 yards but it is so close that it doesn't matter.

Balistic coefficent basically refers to the bullets aerodynamic ability to reduce drag. This number will change depending on the design (boat tail, flat base, round nose, etc...) and the velocity the bullet is fired at. The higher the balistic coefficent number the better the bullets aerodynamic ability wich translates to its ability to retain more velocity and be less effected by wind.

Sectional density basically refers to the ammount of penetration any given bullet will deliver in a straight line. Take a 150 grain bullet out of a 270. It has a sectional density of .279. To get the same sectional density in a 30 caliber bullet you would need roughly a 190 grain bullet. So 150 grains focused on an area that's 277 thousandths of an inch will penetrate better than 150 grains focused on a area that's 308 thousandths of an inch. In theory a bullets of the same sectional density, same construction, and impact velosity will penetrate the same target medium the same distance even though they may be different calibers.


I hope you can understand this and I didn't confuse you too much. If you need better explanation visit these links.

http://www.chuckhawks.com/bc.htm

http://www.chuckhawks.com/sd.htm