8×59mmRb Breda was an Italian heavy arms cartridge. It is unusual in that it is one of the small number of cartridges designed with a rebated rim, meaning the rim of the cartridge is smaller in diameter than the body of the cartridge. The "Rb" in the designation stands for "rebated rim".

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Quick Facts Type, Place of origin ...

8×59mmRb Breda
A Breda cartridge discovered buried in the ground
Type	Machine gun
Place of origin	Italy, Kingdom of Italy
Service history
In service	1935–1960s
Used by	Italy, Portugal[1]
Wars	World War II Portuguese Colonial War[1]
Production history
Designed	1935
Produced	1935–1960s
Specifications
Parent case	unknown
Case type	rebated rim, bottleneck
Bullet diameter	8.36 mm (0.329 in)
Land diameter	8.0 mm (0.31 in)
Neck diameter	9.14 mm (0.360 in)
Shoulder diameter	10.80 mm (0.425 in)
Base diameter	12.49 mm (0.492 in)
Rim diameter	11.92 mm (0.469 in)
Rim thickness	1.40 mm (0.055 in)
Case length	58.84 mm (2.317 in)
Overall length	80.44 mm (3.167 in)
Rifling twist	240[2] or 245[3] mm
Primer type	large rifle
Maximum pressure	3150 atm 46,300 psi
Ballistic performance
Bullet mass/type Velocity Energy 13 g (201 gr) 790 m/s (2,600 ft/s) 4,057 J (2,992 ft⋅lbf) 13.4 g (207 gr) Ball mod. 35 750 m/s (2,500 ft/s) 3,768 J (2,779 ft⋅lbf) 12.57 g (194 gr) AP mod. 39
Source(s): [4][3]

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8×59mmRB Breda was a caliber created for use by the Royal Italian Army in World War II. The cartridge was originally designed for use in anti-aircraft heavy machine guns like the Breda M37, Breda M38, and Fiat–Revelli Modello 1935. It was also used in the experimental Pavesi M42 semi-automatic rifle. It was introduced in 1935 but is no longer in production today.

 Italy manufactured ammunition during the brief period the Breda machine guns were in Italian service.

 Albania manufactured ammunition after World War Two to use in Italian machine guns they captured during World War 2.