.280 British

The .280 British was an experimental rimless bottlenecked intermediate rifle cartridge. It was later designated 7 mm MK1Z, and has also been known as 7 mm NATO, .280/30, .280 Enfield, .280 NATO, 7 mm FN Short, and 7×43mm. It was designed by the British Army in the late 1940s, with subsequent help from Fabrique Nationale in Belgium and the Canadian Army. The .280 British was tested in a variety of rifles and machine guns including the EM-2, Lee-Enfield, FN FAL, Bren, M1 Garand and Taden gun. Despite its success as an intermediate cartridge, the .280 British was not considered powerful enough by the U.S. Army and several variants of the .280 British were created in an attempt to appease the U.S. Army. However, the U.S. Army continued to reject these variants, ultimately adopting the 7.62×51mm NATO.

History
After the Second World War the British, having encountered the new 7.92 "Kurz" cartridge on the battlefield and noted its effectiveness, began a programme to replace the venerable .303 cartridge which had been marked for replacement but had survived as a consequence of wartime pressures on British small arms development. The goal of the British designers was to create a cartridge that would replace all small arms in .303 calibre including the Bren, the No.4 Rifle and the Vickers medium machine gun with a cartridge suitable for a "light rifle". Thus the cartridge had to demonstrate ballistic performance equal to that of a full powered rifle round and yet exhibit as little recoil and blast as possible, so that it was controllable during rapid or automatic fire. A shorter cartridge producing lower recoil also enabled the weapon to be shorter and lighter, and hence easier to use. After extensive tests by the "Ideal Cartridge Panel" in 1945, the British decided upon two 7 mm cartridges – the .270 and the .276. Both designations reflected the measurement of the distance between the rifling lands in the cartridges' respective barrels; the .276 bullet's actual diameter was .284 in. In order to focus their efforts, the British ceased research on the .270 and concentrated their efforts on the .276. The .276 was later renamed the .280 even though no dimensions were changed. Recoil of the .280 cartridge was calculated to be a little under half of the .303. Long range performance actually surpassed that of the .303, and shooters reported that it was much more comfortable to fire with the reduced recoil and reduced blast. It seemed that the British designers had accomplished their goals, and proceeded to introduce the cartridge to their NATO allies.

Despite interest from the Belgians (FN would later produce the .280 in quantity and help improve it) and the Canadians, the Americans were not at all interested, claiming they would not adopt a calibre under .30 inch, or with ballistics inferior to the then-standard .30-06 round. The British attempted to appease the Americans, first with small changes such as changing the rim diameter of the .280 to the size of the .30-06 (resulting in the .280/30 cartridge which was produced in large numbers and is the basis of the dimensions listed to the right). Later, when the .280/30 was rejected by the Americans as being too weak with too great a drop in trajectory, the British and Belgians made large changes to the cartridge design. These resulted in several different variations; one was just a .280/30 with the bullet seated less deeply so more powder could be put in the case, another was a T65 cartridge case necked down to 7 mm. The different cartridges that the British and Belgians eventually came up with fired 140 gr bullets at around 2700 to 2800 ft/s, but with a much greater blast and recoil than the .280/30, which defeated the design parameters of the initial .280 venture. Unsatisfied with the U.S. Army's response on the issue, the British adopted the EM-2 and the .280/30 as their primary rifle and ammunition in 1951 with the .280/30 being re-designated as the "7 mm MK1Z". This effort was to be all in vain, as the Americans adopted the T65 (later to be designated the 7.62×51mm NATO).

A change of government meant that the 7 mm, EM-2 and Taden gun projects were abandoned soon afterwards by Winston Churchill, who returned as the prime minister and desired commonality between the NATO countries. Small amounts of .280 ammunition were later produced during the 1960s for various small arms trials.

The .280 British concept would later prove to have been far ahead of its time, as the U.S. itself adopted an intermediate cartridge — 5.56×45mm NATO — by the end of the following decade. Soon after America's large-scale involvement in Vietnam commenced in 1965 the 5.56 mm ArmaLite AR-15 rifle, later standardised as the M16, was purchased in ever increasing numbers and by the late 1960s had displaced the 7.62 mm M14 in combat units. After insisting on a .30 calibre round with full-power ballistics almost identical to those of the existing .30-06, the U.S. then adopted the 5.56 mm intermediate cartridge, which demonstrated the emergence and dominance of intermediate cartridges on the battlefield (the other notable one being the 7.62×39mm AK-47 round). The adoption of the 7.62×51mm NATO round and the adaptation of the intermediate cartridge CETME (later developed into the G3) and FN FAL designs to fire it, produced rifles that were relatively longer and heavier and had greater recoil. The result was weapons that performed well as longer-range semi-automatic rifles, but were more cumbersome and only marginally controllable in automatic fire. These guns also had a higher training burden and were not well suited to soldiers of smaller stature, again due to the recoil. Coincidentally, in 2002 the Americans developed a military calibre intended for the M4 version of the M16 family called the 6.8 mm Remington SPC — with similar ballistic properties to the .280 British cartridge — which was intended to provide better ballistics than the 5.56×45mm.

During the late 1960s, experiments took place in the U.K. to design an ideal military small-arms round. It started with calculations of the bullet energy required to inflict a disabling wound on soldiers with various levels of protection. Large calibers were found to need more energy to push through armor. A range of "optimum solutions" were produced ranging from 4.5 mm to 7 mm. The preferred solution was a 6.25 mm bullet housed in a necked-down .280 case. While the 7.62 NATO required 700 J of force on impact to penetrate helmets and heavy body armor, the 6.25 mm needed only 580 J of impact force. It had a 100 gr bullet with a muzzle velocity of 2,680 ft/s and 2,160 J of muzzle energy. Tests found that the 6.25 mm cartridge matched the 7.62 NATO in penetration out to 600 m and remained effective for a longer distance, while producing recoil close to that of the 5.56 mm. However, it was not designed for very long range and its bullet was relatively light. Testing of the 6.25×43mm was conducted from 1969 to 1971, when development ceased in favor of the smaller 4.85x49mm.

Specifications
Types of bullets and colours of tips:
 * AP (130 gr)
 * API (130 gr): black
 * Ball (130 - 140 gr): plain (unmarked), green, pink, yellow, brown
 * Observation (130 gr) (6 gr WP): red
 * Tracer (130 gr): white

Note: Most cartridges have been observed with a purple annulus. Several experimental cartridge cases were made out of aluminium, in various colors including orange.

Known manufacturers:
 * Radway Green
 * Fabrique Nationale
 * Kynoch

Performance
The following comparisons are excerpts from a manual published by the "Small Arms Group Armament Design Establishment" from the Ministry of Supply:

Variants

 * .270 British: Designed at the same time as the .280. It has a slightly smaller bullet diameter of .279 in (versus .284 in for the .280) but a lighter bullet (93 to 100 gr) with a greater muzzle velocity (2750 –), longer case (1.8 in) and shorter overall length (2.45 in). Research was abandoned in 1948.
 * 7 mm "Optimum": The original .280 round with the bullet seated less deeply, giving an overall length of 2.6 in.
 * 7 mm "High Velocity": Longer case (1.95 in), with an overall length of 2.79 in. Similar 140 gr bullet fired at 2750 ft/s.
 * 7 mm "Compromise" (aka T65/7 mm): Necked down T65 (7.62×51mm NATO) to 7 mm. Case length 2 in, overall length 2.8 in, similar 140 gr bullet fired at 2800 ft/s.
 * 7 mm "Second Optimum" (7×49 mm): Designed by FN. Also known as the 7 mm "Medium" and the 7 mm "Liviano". FN would later sell FAL rifles chambered in this calibre along with a sizeable amount of ammunition to Venezuela. Longer case (1.935 in) with an overall length of 2.78 in. 140 gr bullet fired at 2755 ft/s.
 * 6.25 mm (6.25×43 mm): A British experimental cartridge designed during the early 1970s, using the .280/30 as a parent case, which was necked down to fit a smaller bullet.

Comparable cartridges
For .280:
 * 7×44mm Danish, a Danish experimental cartridge fired by the Weibel M/1932 tested in 1936.
 * 7 mm Bench Rest (wildcat cartridge, at one time produced by Remington Arms)
 * .308×1.5" "Barnes" (wildcat)
 * .308×1.75" and necked down 7 mm variant (wildcats)

For 7 mm HV, 7 mm Compromise, 7 mm Second Optimum:
 * 7mm-08 Remington