|Place of origin||22x20px United Kingdom|
|Designer||Royal Small Arms Factory|
|Parent case||5.56×45mm NATO|
|Case type||Rimless, bottleneck|
|Bullet diameter||.197 in (Script error mm)|
|Neck diameter||.220 in (Script error mm)|
|Shoulder diameter||.353 in (Script error mm)|
|Base diameter||.375 in (Script error mm)|
|Rim diameter||.376 in (Script error mm)|
|Rim thickness||.041 in (Script error mm)|
|Case length||1.925 in (Script error mm)|
|Overall length||2.455 in (Script error mm)|
|Primer type||Small Rifle|
|Maximum pressure||52,000 psi|
|55 gr (Script error g) FMJ||3,115 ft/s (Script error m/s)||1,190 ft·lbf (Script error J)|
| Test barrel length: N/A|
Source(s): Ammo Encyclopedia
The 4.85x49mm cartridge is based on the 5.56x45mm 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.
During the 1960s, the United Kingdom experimented with creating a lightweight but effective replacement for the 7.62x51mm NATO round. Their original experiments focused on a .280 British round necked downed to 6.3mm. However, in the 1960s, a West German study proposed that an ideal cartridge would have a 5mm or smaller caliber. The results of this study encouraged the United Kingdom switch to using a 5mm caliber 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 4.85x49mm originally started off as the 5x44mm round, which was made in 1970. The bullet shape used in these early prototypes were based on one used by the 6.23x43mm 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 “4.85x44mm” 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 4.85x49mm round. However, before the production lines were fully retooled for the new round, RSAF Enfield required a batch of ammo for testing. Existing 4.85x44mm rounds had their neck manually stretched out 5mm in order to qualify for the test.
Tests with both the 4.85x49mm round and the L64/65 continued throughout the 1970s. In 1976, the L64/L65 weapon system was officially announced, revealing the first time that the public officially knew about it and the 4.85mm cartridge. In 1977, trials to find a new cartridge and weapon for NATO standardization went underway. The United Kingdom submitted the IW weapon a 4.85x49mm. 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 round had over the 5.56 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 favor 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/s.
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 4.85x44mm 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.
A special plastic training dummy version of the 4.85mm was also made. it consisted of a sawed-off 4.85mm cartridge with a blue plastic head on it. When the gun is fired, the plastic head flies off.
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.
Armor piercing rounds were developed for both the 4.85x44mm and 4.85x49mm rounds, but never went into large-scale production, like the ball and tracer variants were. The AP rounds have a black band just under the bullet tip.