|Place of origin||United States|
|Used by||United States|
|Case type||Rimless, bottleneck|
|Bullet diameter||.308 in (7.8 mm)|
|Neck diameter||.340 in (8.6 mm)|
|Shoulder diameter||.441 in (11.2 mm)|
|Base diameter||.470 in (11.9 mm)|
|Rim diameter||.473 in (12.0 mm)|
|Rim thickness||.045 in (1.1 mm)|
|Case length||2.54 in (65 mm)|
|Overall length||3.34 in (85 mm)|
|Primer type||Large rifle|
The .30-03 was a short-lived cartridge developed by the United States in 1903, to replace the .30-40 Krag in the new Springfield 1903 rifle. The .30-03 was also called the .30-45, since it used a 45 grain (2.9 g (0.10 oz)) powder charge; the name was changed to .30-03 to indicate the year of adoption. It used a 220 grain (14 g (0.49 oz)) roundnose bullet. It was replaced after only three years of service by the .30-06, firing a Spitzer bullet giving better ballistic performance.
The .30-03 was developed to replace the .30-40 Krag cartridge used in the Krag-Jørgensen rifle, which was the first bolt action rifle adopted by the US military, and the first that used smokeless powder. The Krag-Jørgensen rifle had some serious limitations compared to the new Mauser rifles being used by European armies; it was loaded one round at a time, rather than using a stripper clip, and the Krag-Jorgensen's single locking lug on the bolt made the action much weaker than the strong, two lug Mauser bolt, limiting the power of the round. A new rifle was designed, using the Mauser as a guide, and a new cartridge was designed for it. The new cartridge was more powerful, using a 45 grain (2.9 g) charge of smokeless powder, 5 grains (0.3 g) more than the .30-40. The bullet was the same, a .30 caliber, 220 grain (14 g) round nosed jacketed bullet, at a higher velocity of 2300 feet per second (700 m/s), compared to the 2000 feet per second (610 m/s) of the .30-40 Krag. The new rifle was also the first in a trend of shorter infantry rifles; the 24 in (610 mm) barrel was halfway between the standard rifle and the carbine used by the cavalry, and thus there was no carbine variant of the 1903 rifle. The .30-03 cartridge was also a rimless design, which allowed better feeding through the box magazine than the old .30-40 Krag case. The Model 1895 Winchester lever action rifle was offered in 30-03 from 1905, but sold poorly in comparison to the .30-06 chambering offered in 1908.
The .30-03 cartridge suffered from the start. It caused severe erosion of the bore of the rifle, due to the high pressures and temperatures needed to push the heavy bullet to the desired velocity. The heavy bullet was also an issue; the 220 grain (14 g) bullet was aerodynamically inefficient and had a very curved trajectory (see external ballistics) so it was not well suited for long range shots. It was also unfashionable, since most countries were switching to a 7 or 8 mm cartridge firing a lighter, around 150 grains (9.7 g), spitzer pointed bullet at a higher velocity. This gave better energy retention and a flatter trajectory. The .30-03 was shortened slightly by 0.07 inches (1.8 mm) in the neck, the powder was reformulated to burn cooler, and the bullet was changed to a 150 grain (9.7 g) spitzer bullet, creating the .30-06 cartridge.
Since the new .30-06 was shorter than the .30-03, it could fire in 1903 rifle, but with poor accuracy. The 1903 rifles were all recalled, fitted with the Model of 1905 sights and bayonet, and rechambered for the new .30-06 cartridge. This last procedure was done by unscrewing the barrels, milling off the end of each chamber, re-threading the barrels, rechambering them and screwing them back on the same actions. This ended the short life of the .30-03; out of nearly 75,000 made, no more than a handful of original 1903 rifles escaped the conversion to .30-06 (estimates range from 50 to 100 rifles), becoming rare collectors items. Even the .30-03 cartridge is a rarity, found only in collections of rare cartridges. The .270 Winchester  cartridges were based on reducing the neck diameter of a .30-03 cartridge case to retain a similar bullet-holding length with the same shoulder.
- Cartridges of the World (11th Edition), Frank C. Barnes, Edited by Stan Skinner, Gun Digest Books, 2006, ISBN 0-89689-297-2 pp.130,164
- 30.06 Reload Information at Reloading Bench with some information on original .30-03 ballistics and the .30-40 Krag it replaced[self-published source]
- Sharpe, Philip B. (1953). Complete Guide to Handloading (3rd ed.). New York: Funk & Wagnalls. p. 374.
- Canfield, Bruce N. (2006). "From Poor Invention To America's Best". American Rifleman (National Rifle Association) 154 (September): 59–61,91–92&94.
- Pictures and information on the development of the .30-06 from the .30-03 at the Cartridge Collectors Exchange.