|Place of origin||United Kingdom|
|Designer||Royal Small Arms Factory|
|Parent case||5.56×45mm NATO|
|Case type||Rimless, bottleneck|
|Bullet diameter||.197 in (5.0 mm)|
|Neck diameter||.220 in (5.6 mm)|
|Shoulder diameter||.353 in (9.0 mm)|
|Base diameter||.375 in (9.5 mm)|
|Rim diameter||.376 in (9.6 mm)|
|Rim thickness||.041 in (1.0 mm)|
|Case length||1.925 in (48.9 mm)|
|Overall length||2.455 in (62.4 mm)|
|Primer type||Small Rifle|
|Maximum pressure||52,000 psi|
|Test barrel length: N/A|
Source(s): Ammo Encyclopedia
The 4.85×49mm cartridge is based on the 5.56×45mm NATO, but uses a 5mm bullet and has a longer neck than the 5.56mm does. Muzzle velocity is better than the M193 5.56mm loading, which this cartridge was designed to compete against. The 4.85×49mm cartridge weighed 11.62 grams (179.3 gr).
During the 1960s, the United Kingdom experimented with creating a lightweight but effective replacement for the 7.62×51mm NATO round. Their original experiments focused on a .280 British round necked down to 6.3mm. However, in the 1960s, a West German study proposed that an ideal cartridge would have a 5mm or smaller calibre. The results of this study encouraged the United Kingdom switch to using a 5mm calibre bullet for their experimental cartridge. The requirement for a 5mm round for what would be the SA80 sealed the idea that a 5mm round needed to be made.
The 4.85×49mm originally started off as the 5×44mm round, which was made in 1970. The bullet shape used in these early prototypes were based on one used by the 6.23×43mm round, another experimental British round. The actual cases were made from reformed 5.56 NATO rounds. However, it was soon decided that the round would be renamed to “4.85×44mm” in order to match the diameter of the test gun barrel's lands. The actual diameter of the round didn't change.
Continued tests showed that there were problems with bullet seating. To fix this, the round's neck was elongated 5mm to create the 4.85×49mm round. However, before the production lines were fully retooled for the new round, RSAF Enfield required a batch of ammo for testing. Existing 4.85×44mm rounds had their neck manually stretched out 5mm in order to qualify for the test.
Tests with both the 4.85×49mm round and the L64/65 continued throughout the 1970s. In 1976, the L64/L65 weapon system was officially announced to the public. In 1977, trials to find a new cartridge and weapon for NATO standardisation went underway. The United Kingdom submitted the IW weapon a 4.85×49mm. Lots of both the XL1E1 ball and XL2E1 tracer round were created in order to provide enough ammunition for the tests. The UK hoped that the United States and NATO would see the inherent advantages the 4.85×49mm round had over the 5.56×45mm NATO round and adopt it.
The 4.85mm's lifespan came to an end when the ending results of the NATO tests concluded that the FN Herstal SS109 bullet for the 5.56mm had the best performance. In 1979, British testers formally scrapped the 4.85mm round in favour of the 5.56mm round. The IW system was subsequently rechambered to 5.56mm.
No other countries have used the 4.85mm round.
Several variants of the 4.85mm round were made over its lifetime.
The most common type of 4.85mm round out there is the XL1E1 Ball, which was used in NATO trials. This round has a 55.3 grain bullet that has a muzzle velocity of 3,115 ft/s and a muzzle energy of 1,210 ft/lbf.
Several tracer types were made for the 4.85mm, but the most common one is the XL2E1, which was used in NATO trials. It has an orange tipped head. Up to ten other variants were produced, but never made it into full production.
A 4.85mm variant designed for short range used the same case that the standard round used, but fired a round and white plastic bullet.
Several dummies were produced for the 4.85mm during its lifetime. Early dummies were simply a blank 4.85×44mm round with a 5mm longer neck, but later models include a round with three holes drilled in its base, and a chrome-plated case that has several vertical flutes on it.
Early blanks were made out of, but later ones used a standard-shaped cartridge with a rosecrimp blank shape where the head would be. The rosecrimp blank was also used for blanks used to fire rifle grenades.
- Bussard, Mike (2011). Ammo Encyclopedia 2nd Edition. Minneapolis, MN: Blue Book Publications, Inc. p. 498. ISBN 978-1-936120-01-7.
- "The 6.25x43mm". Retrieved 2012-09-26.
- "The 5x56x45mm timeline: 1970–1973". Archived from the original on 2012-09-25. Retrieved 2012-09-26.
- "The 4.85mm Cartridge". Retrieved 2012-09-26.
- "SA80 (Small Arms for the 1980s): The Sorry Saga of the British Bulldog's Bullpup". Retrieved 2012-09-26.
- "The 5x56x45mm timeline: 1974–1979". Archived from the original on 2012-09-25. Retrieved 2012-09-26.