Caliber is the diameter of the bullet and the diameter of the bore of a rifle.

IE............... a 30 caliber bullet is actually 308 thousandths of an inch in diameter.

A cartridge is the bullet, case, powder, and primer all put together.

Many cartridges use the same bullet diameter and many will use different numbers for the same diameter bullet. Such as the 300 magnum and 308 Winchester. They both use .308 diameter bullets but the 300 is named what it is because the rifleing in a barrel is typically 4 thousandths of an inch tall and you have two sides so that equals 8 thousandths of an inch which gives you the 300 (.308 - .008 = .300)



You will also find out that some bullet diameters are no where close to what their name would suggest.

Such as a 7mm bullet. The actual bullet diameter of a 7mm bullet is .284 inches but a true 7mm equals .276 inches which is actually .001 inches smaller than a .277 inch bullet that the 270 Winchester uses.

Another good one is the 44 caliber bullet from a 44 mag and 444 marlin. It is actually .429 inches in diameter. How they got 44 from .429 is beyond me but they did.


The best thing you can do is do a lot of reading and ask us a lot of questions. Cartridges of the world is an excelent book. It gives you a brief history of most cartridges made, a drawing of the cartridge and usually gives you a few velocities with different weight bullets. Chuck hawks web site is full of information as well.