20×138mmB

The 20×138mmB or Long Solothurn cartridge is a type of ammunition used mainly for anti-aircraft and anti-tank weapons during World War II. The designation means the caliber is 20 mm, the length of the cartridge case is 138 mm and B indicates it is a belted case. The loaded cartridge weighs 300 grams (10.7 oz).^[1]

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]

History

Three Finnish and Italian 20×138B cartridges next to a 37mm anti-tank shell

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

Weapon platforms

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

Switzerland

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

Germany

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

Italy

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

Finland

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

Poland

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