20×138mmB
20×138B cartridge and a tape measure in centimeters
Type	Anti-armor/anti-air
Place of origin	Switzerland
Service history
Used by	Switzerland,Germany,Italy,Finland,Poland
Wars	World War II
Production history
Designed	1930
Manufacturer	Swiss Solothurn
Variants	Long Solothurn
Specifications
Case type	Bottleneck, belted
Bullet diameter	20 mm
Neck diameter	20.9 mm (0.82 in)
Shoulder diameter	25.5 mm (1.00 in)
Base diameter	26.86 mm (1.057 in)
Rim diameter	28.48 mm (1.121 in)
Rim thickness	26.86 mm (1.057 in)
Case length	138 mm (5.4 in)
Overall length	202.7 mm (7.98 in)
Ballistic performance
Bullet mass/type Velocity Energy 120 grams (4.1 oz) 900 metres per second (2,950 ft/s) 47,000 J (34,655 ft⋅lbf)[1]

The20×138mmB orLong Solothurn cartridge is a type of ammunition used mainly foranti-aircraft andanti-tank weapons duringWorld War II. The designation means thecaliber is 20 mm, the length of the cartridge case is 138 mm andB indicates it is abelted case. The loaded cartridge weighs 300 grams (10.7 oz).^[1]

The 20×138mmB cartridge was developed by theWaffenfabrik Solothurn, a Swiss front company ofRheinmetall in the early 1930s from a less powerful cartridge20×105mmB cartridge.

The 20×138mmB cartridge is used in the following weapons:

• Solothurn anti-tank rifles:S-18/1000 andS-18/1100
• SolothurnST-5 20mm AA Gun

• FlaK 30 andFlaK 38 single-barrel, andFlakvierling quadruple-barrel anti-aircraft guns
• KwK 30 andKwK 38 vehicle-mounted weapons
• MG C/30L aircraft gun

• Cannone-Mitragliera da 20/65 modello 35 (Breda)
• Cannone-Mitragliera da 20/77 (Scotti)

• Lahti L-39 anti-tank rifle
• Lahti L-40 anti-aircraft gun

• Nkm wz.38 FK anti-tank vehicle-mounted gun

Wikimedia Commons has media related to20 x 138 mm.

• Large-caliber cartridges
• 20 mm artillery
• Military equipment introduced in the 1930s

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