page_title: 55 S 55
section_title: Design
hierarchical_section_title: 55 S 55 / Design
caption_attribution_description: Suomi: Description Suomi: Singon S 55 S tähtäimen kaavakuvaDate 1960Source Panssarintorjuntaohjesääntö I osa s.122Author N.o2121/Ohjeisto/8b Suomi: Singon S 55 S tähtäimen kaavakuva
context_page_description: 55 S 55, colloquially kevyt sinko and nicknamed Nyrkki, was a Finnish recoilless anti-tank weapon from the mid-1950s. The 55 S 55 was designed by a Finnish Defence Forces team led by MSc, Capt Esko Puronto, and it was manufactured by FDF's Vammaskoski factory.
context_section_description: The main principle in the 55 S 55 is that of a smoothbore recoilless gun with a venturi effect recoil damper. It is developed based on the Panzerfaust, and is similar to the Swedish (Carl Gustaf recoilless rifle), German (Panzerfaust 2) and Soviet (RPG-2) designs of the time, though its design was not influenced by them. Like the Carl Gustaf, the projectiles of the 55 S 55 aren't rocket propelled; all of the forward momentum is gained from the propellant charge, which burns immediately at the launch.
  The 89 millimetre HEAT grenade weighs 2.3 kg, and is capable of penetrating 300 millimetres of RHA +/- 40 millimetres. The fuse is able to function at as small as a 20 degree angle of impact. The longest recommendable distance for stationary armour targets is 300 metres and to moving targets 200 metres. 55 millimetre fragmentation and incendiary WP grenades as well as illumination rounds and 55 millimetre solid training ammunition were also available. The fragmentation and training ammunition weighed also 2.3 kg, and had the same 160 m/s muzzle velocity as the HEAT grenade.  If capped, the fragmentation grenade can penetrate obstacles such as light doors, bushes and windows before exploding. These can be shot up to 700 metres against stationary targets. A rifle calibre practice barrel chambered in 7.62×54mmR could be installed inside the launching tube.
  The backblast from the 55 S 55 is lethal or highly dangerous up to 7 metres; gravel, small rocks and other small objects could be propelled up to 15 metres behind. The gunner should have at least two metre clearance behind, so the backblast wouldn't be deflected back to the shooter; shooting from an enclosure was forbidden.
  The sights are optical; three types of different optical sights exist (Kr, D and NE), of which two (Kr and D) share the same reticle; the NE sight has a stadiametric rangefinder reticle. There's provision for illuminating the reticle and the stadia marks in the NE sight.
  The 55 S 55  was the standard anti-tank weapon of the Finnish Army from the late 1950s but has been phased out since the 1980s giving way to
  M72 LAW and Apilas. The weapon was operated by a two-man team, loader and the gunner.
  The main disadvantage of the weapon was low muzzle velocity resulting in an arched trajectory. This exposed the grenade to wind conditions and branches in covered terrain.
  Also the smoke and noise when firing could reveal the location making the user(s) a target. The weapon had a tendency to nod on launch requiring careful handling.
caption: Sight picture of the 55 S 55 NE sight.
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