The 5.56x45mm:

In the late sixties The 5.56x45mm round was introduced for the first time in British service. The cartridge was used by the Royal Marines together with the american M16A1 rifle. The ball cartridges were of the blunt ogive M193 type. The M16 rifle did not replace the L1A1 service rifle and was only used in smal numbers.
A decate later in the late seventies / early eighties The North Atlantic Treaty Organisation (NATO) had decided to abandon the 7.62x51mm round in favor of a new ultra small round for future use. The new round would be selected after several tests conducted by NATO. The United Kingdom was entering these tests with a new developed cartridge, the 4.85mm round. Finaly NATO selected the 5.56mm cartridge as the NATO standard round for the future. The developement of the 4.85mm round was stopped in favor of the 5.56mm cartridge.
By converting the Individual Weapon into a 5.56mm weapon, the L85A1, the British army started to use the 5.56 round on a large scale.
A wide range of different cartridges were developed and these are shown here below:

Ball ammunition:

               

ball M193, ball L2A2 with there headstamps; RG 5.56 82 and RG 87 [+]

Ball packages:

Tracer ammunition:

                

tracer round with headstamp (RG 86 [+]) (and box)

Blank ammunition:

                                  

blank L1A1 and L1A2, with headstamp; RG 86 L1A1 and RG 93 L1A2 (and boxes)

Drill ammunition:

                         

Drill rounds; with headstamps...(and box)

Royal Ordnance Training Ammunition (ROTA):

        
For training purposes a short range bullet was developed at Radway Green. (and box)