SOMETIMES standard overall length — the overall length to which factory cartridges are loaded — doesn’t suit your purpose. In a bolt-action repeater, the length of the chamber throat dictates the overall length of your handloads, but quite often the magazine may be long enough to allow bullets to be seated out farther. A major concern, of course, will be the relationship of the bullet to the chamber throat when the loaded cartridge is fully chambered.
If you want to seat the bullet out farther you get a gunsmith to lengthen the throat to suit. The increased distance of free bullet travel is known as free-bore.
The reason that Weatherby cartridges use larger powder charges than other cases with similar bore diameters and bullet weights is due not to case capacity but to free-bore throating. Free bullet travel reduces initial resistance and pressures, thus allowing more powder to be used to build up the same pressures as given by other cartridges. This usually results in a slight velocity increase if pressures are the same when using the same powder charge and bullet.
All my personal hunting rifles have been free-bored and they are all consistently accurate.
By definition, the throat (also called the lede or bullet seat)
