Overbore

Overbore cartridges are those with a relatively large case volume or case capacity, coupled with a relatively small diameter bullet.

As the ratio is expressed in units of length, relatively high Oratio is a good predictor of suitability for relatively long barreled guns.

Oratio is also used to predict barrel life in cartridges of the same caliber, but not of different calibres, since the ratio is an extensive quantity that does not correlate to temperature or pressure (e.g. a .50 cal straight cartridge may have the same overbore as a highly necked down .17 cal cartridge).

The bore cross section areas "Q" used in the calculations were taken from the appropriate C.I.P.

The intermediate cartridges .30 Carbine, 7.92×33mm Kurz, 7.62×39mm, 7.62×45mm, 5.45×39mm, .223 Remington/5.56×45mm NATO and 5.8×42mm stand out as having relatively low sub 8 Oratio's.