|Place of origin|| Australia|
|Parent case||.303 British|
|Case type||Rimmed, bottleneck|
|Bullet diameter||0.257 in (Script error mm)|
|Neck diameter||0.290 in (Script error mm)|
|Shoulder diameter||0.412 in (Script error mm)|
|Base diameter||0.460 in (Script error mm)|
|Rim diameter||0.540 in (Script error mm)|
|Rim thickness||.064 in (Script error mm)|
|Case length||2.185 in (Script error mm)|
|Overall length||2.85 in (Script error mm)|
|Case capacity||50.86 gr H2O (3.306 cm³)|
|Rifling twist||1-12 inches|
|Primer type||Large rifle|
|87 gr (Script error g) SP||3,010 ft/s (Script error m/s)||1,750 ft·lbf (Script error J)|
|100 gr (Script error g) HPBT||2,800 ft/s (Script error m/s)||1,740 ft·lbf (Script error J)|
|117 gr (Script error g) SP||2,800 ft/s (Script error m/s)||1,740 ft·lbf (Script error J)|
| Test barrel length: 24|
Source(s): Reload Bench 
The .303/25, sometimes known as the .25/303 is a wildcat centrefire rifle cartridge, based on the .303 British, necked down to fire a .257 projectile, originating in Australia in the 1940s as a cartridge for sporterised rifles, particularly on the Lee Enfield action, similar versions also appeared in Canada around the same time.
The .303/25 was very popular for a number of reasons, one being that the .25 caliber was better suited to small game than the .303, the rifles were cheap and plentiful and in New South Wales ownership of military cartridges was severely restricted. Several versions existed but most were simply necked down and remained full length. Although Lee Enfields were the most common, conversion of other rifles mostly suited to rimmed cartridges such as P14 Enfield, Martini Enfield, 1885 and 1895 Winchesters were often seen, as well as 98 and 96 Mausers.
Loaded ammunition and brass was produced by the Super Cartridge Company, Riverbrand, ICI and Sportco, some using new Boxer primed cases, others using military Berdan primed cases. Cases can be formed simply by necking down .303 British brass available from Remington, Federal, Winchester, Sellier & Bellot and others. Reloading dies are made by most larger manufacturers, like RCBS, Lyman, CH and Simplex.