|Place of origin||United Kingdom|
|Case type||rimless, bottleneck|
|Bullet diameter||.282 in (Script error mm)|
|Base diameter||.528 in (Script error mm)|
|Rim diameter||.517 in (Script error mm)|
|Case length||2.35 in (Script error mm)|
|Overall length||3.23 in (Script error mm)|
|165 gr (Script error g)||2,800 ft/s (Script error m/s)||2,888 ft·lbf (Script error J)|
Several developmental versions of ammunition were prepared beginning in 1910 before approximately 1,000 P'13 rifles with 600,000 rounds of RL18000C trials cartridges were distributed to troops in 1913. The troops' trials rifles and ammunition were distributed to the musketry school at Hythe, to one squadron in each of three cavalry regiments, and to one company in each of eight infantry battalions. One of the cavalry squadrons was stationed in South Africa and one of the infantry companies was stationed in Egypt. The remainder of the units were in the United Kingdom. Cartridges were packaged in 5-round stripper clips similar to those used by Mauser and M1903 Springfield rifles. Ball ammunition was loaded with 49.3 grains of cordite behind 165-grain cupronickel-jacketed spitzer bullets. Drill rounds containing no primer or powder have been reported in two versions. One has a tin-plated case with the standard bullet, and the other has a round-nose wood bullet with an unplated brass case. 
The troop trials reported the cartridge produced heavy recoil with undesirable muzzle flash and overheated rifle barrels. Overheating caused excessive barrel wear and some potentially dangerous pressure indications from cartridges pre-heated in hot barrels before firing. Rather than confront continued development of a new cartridge simultaneously with inevitable wartime production problems, the United Kingdom continued manufacturing .303 British caliber Lee-Enfield rifles as the standard military arm through the first world war. Canada, on the other hand, had some experience with the similar .280 Ross cartridge and appears to have taken interest in potential use of the P'13 rifles to arm newly mobilized troops. Canada contracted with Winchester Repeating Arms to manufacture ammunition until more suitable rifles became available for standard issue.
Ammunition is known to have been manufactured by:
- Royal Laboratory (headstamped R^L)
- Kings Norton Metal Company (headstamped KN, some with date 13)
- Greenwood & Batley (headstamped GB or G&B)
- Kynoch (headstamped K)
- Winchester (headstamped WRA Co 8-16)
The P'13 rifle design was modified as the Pattern 14 Rifle (P'14) chambered for the .303 British cartridge. Production was initially assigned to Vickers; but tooling was shortly passed to United States manufacturers so Vickers could focus on machine gun production. Remington Arms and Winchester manufactured 1,233,075 P'14 rifles for the United Kingdom in 1915 and 1916. Remington subcontracted the largest share of production to the Baldwin Locomotive Works plant in Eddystone, Pennsylvania. The design was modified again as the M1917 Enfield rifle chambered for the .30-06 Springfield cartridge. Remington, Winchester and Baldwin manufactured 2,193,429 M1917 rifles for the United States. Approximately 75% of the American Expeditionary Forces carried M1917 rifles into combat. Nearly half of these M1917 rifles were sent to the United Kingdom as Lend-Lease in the early days of World War II. Remington modified the design again as the basis of their model 30, 30S, and 720 rifles for civilian production.
The .276 Enfield case was necked up to .303 caliber for various armor-piercing bullet tests conducted in the United Kingdom between 1922 and 1935.