the bolt face when the action is closed. The cartridge is said to be rimless if the extractor groove is machined into the head of the case so the rim is the same diameter as the adjacent part of the case. Most modern automatic firearms use rimless cartridges. Straight-walled rimless cartridges often headspace on the forward lip of the cartridge as shown in the diagram at the top of this article. This necessitates careful attention to consistent case length. Bottle-necked rimless cartridges may headspace on the conical shoulder between the narrow neck and the larger diameter portion of the case. Some large rimless magnum cartridges have a belt formed above the extractor groove. This belt is of slightly larger diameter than the adjacent case, so the cartridge can headspace from the forward edge of the belt closest to the bullet. The original purpose of the belt was to give accurate headspacing for cartridges with shallow shoulder angles, where longitudinal precision of seating using such a shoulder presents difficulties. In effect this was similar to the headspacing function of a rim, but gave a long enough surface for cartridges to lie side-by-side in a magazine without risk of interference during the feed-stroke. The adoption of the belt as headspacing feature on rounds such as the .300 H&H Magnum and its derivatives ultimately started a fashion that resulted in most later magnum rifle cartridges featuring belts. Some more or less straight cartridges have no bottleneck on which to headspace. Such cylindrical shaped cartridge cases use the case mouth (the forward end of a cartridge case) as a forward positioned flange used for headspacing. C.I.P. ammunition approval procedure and headspace The standards organization Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives (Permanent International Commission for Firearms Testing - commonly abbreviated as C.I.P. or CIP) uses a rimless, rimmed, magnum, pistol and revolver and rimfire cartridges classification to differentiate between hundreds of different small arms chamberings. The dimensional checking of the ammunition, as described in the C.I.P. Decisions, Texts and Tables, is left to the manufacturers themselves. During C.I.P. ammunition approval headspace is not checked, even on rimless cartridges with taper. The view is that in the very unlikely case (according to the current quality standards) the cartridge is too long, once pressed by the bolt, the pressure will rise too high causing rejection. If it is too short, firing will fail