and the receiver may stretch, all causing the headspace to gradually increase from the factory specifications measured by the "go" and "no-go" gauges. A bolt that closes on "no-go" but not on "field" is close to being unsafe to fire, and may malfunction on cartridges that are slightly out of specification. Headspace gauges are typically used by inserting the gauge into the bolt face engaging the extractor claw and then into the firearm chamber, and noting upon which gauge the bolt fully closes, and which it does not. The closing force applied to the bolt on a bolt-action firearm when making these assessments should be consistently and lightly applied; otherwise, an incorrect assessment of headspace will result if the bolt is forced close with excessive pressure. The below table illustrates the function of each gauge: Other cartridge dimensions Headspace is not the only important cartridge dimension. Other dimensions like overall cartridge length and base diameter are also significant for proper fit of a cartridge into a firearm, and may be included as part of a headspace gauge. Cartridges very close to chamber dimensions generally offer superior accuracy, but slightly undersized cartridges load more smoothly and reliably under variable temperature conditions or when fouling accumulates in the chamber or cartridges become corroded. A firearm chamber for rimmed ammunition will often have two small ledges or steps. One at the rear engages with the forward face of the rim, as the rim-stop. The other step in the front of the chamber accommodates the thickness of the case wall at the forward edge of the case neck where the projectile emerges as a close fit to the beginning of the bore, the throat or leade. If the case length is too long, then the bolt on closing pushes the case over the forward step of the chamber at the throat / leade and can crush or crimp the case around the projectile at the neck of the case, leading to all sorts of performance, pressure and safety problems. Many target shooters who use rimmed ammunition, such as .303 British, will carefully sort the cases by headstamps into groups of the same make or batch, then gauge the thickness of the case rim into lots of the same, or very close, rim thickness. They then keep the fire-formed cases which are now optimised in shape to that firearm chamber, thereby increasing the accuracy potential