Editing Handloading (section)

===Headspace gauges and modified case gauges===

[[File:Miscellaneous headspace guages.jpg|thumb]]
Bottleneck rifle cartridges are particularly prone to encounter incipient head separations if they are full-length re-sized and re-trimmed to their maximum permitted case lengths each time they are reloaded.  In some such cartridges, such as the [[.303 British]] when used in Enfield rifles, as few as 1 or 2 reloadings can be the limit before the head of the cartridge will physically separate from the body of the cartridge when fired.  The solution to this problem, of avoiding overstretching of the brass case, and thereby avoiding the excessive thinning of the wall thickness of the brass case due to case stretching, is to use what is called a "headspace gauge".  Contrary to its name, it does not actually measure a rifle's [[headspace (firearms)|headspace]].  Rather, it measures the distance from the head of the cartridge to the middle of the shoulder of the bottleneck cartridge case.  For semi-automatic and automatic rifles, the customary practice is to move the midpoint of this shoulder back by no more than 0.005 inches, for reliable operation, when resizing the case.  For bolt-action rifles, with their additional camming action, the customary practice is to move this shoulder back by only 0.001 to 0.002 inches when resizing the case.  In contrast to full-length resizing of bottleneck rifle cartridges, which can rapidly thin out the wall thickness of bottleneck rifle cartridges due to case stretching that occurs each time when fired, partial length re-sizing of the bottleneck case pushes shoulders back only a few thousandths of an inch will often permit a case to be safely reloaded 5 times or more, even up to 10 times, or more for very light loads.

[[File:Modified case and ogive guage..jpg|thumb]]
[[File:Modified case and ogive guage in use.jpg|thumb|Modified case and ogive guage in use]]
Similarly, by using modified case gauges, it is possible to measure precisely the distance from a bullet [[ogive]] to the start of rifling in a particular rifle for a given bottleneck cartridge.  Maximum accuracy for a rifle is often found to occur for only one particular fixed distance from the start of rifling in a bore to a datum line on a bullet ogive.  Measuring the overall cartridge length does not permit setting such fixed distances accurately, as different bullets from different manufacturers will often have a different ogive shape.  It is only by measuring from a fixed diameter point on a bullet ogive to the start of a bore's rifling that proper spacing can be determined to maximize accuracy.  A modified case gauge can provide the means by which to achieve an improvement in accuracy with precision handloads.

Such head space gauges and modified case gauges can, respectively, permit greatly increasing the number of times a rifle bottleneck case can be reloaded safely, as well as improve greatly the accuracy of such handloads. Unlike the situation with using expensive factory ammunition, handloaded match ammunition can be made that is vastly more accurate, and, through reloading, that can be much more affordable than anything that can be purchased, being customized for a particular rifle.