2 . 8 cm sPzB 41 2 . 8 cm " schwere Panzerbüchse " 41 ( sPzB 41 ) or " Panzerbüchse 41 " was a German anti - tank weapon working on the squeeze bore principle . Officially classified as a heavy anti - tank rifle ( German : " schwere Panzerbüchse " ) , it would be better described , and is widely referred to , as a light anti - tank gun . Description . Although the sPzB 41 was classified as a heavy anti - tank rifle , its construction was much more typical of an anti - tank gun . Like the latter , it had a recoil mechanism , carriage and shield . The only significant feature the weapon had in common with anti - tank rifles was a lack of elevation and traverse mechanisms — the light barrel could be easily manipulated manually . The design was based on a cone - shaped barrel , with the caliber reducing from 28 mm at the chamber end to only 20 mm at the muzzle . The projectile carried two external flange s ; as it proceeded toward the muzzle , the flanges were squeezed down , decreasing the diameter with the result that pressure did not drop off as quickly and the projectile was propelled to a higher velocity . The barrel construction resulted in a very high muzzle velocity - up to 1 , 400 m / s . The bore was fitted with a muzzle brake . The horizontal sliding breech block was " quarter - automatic " : it closed automatically once a shell was loaded . The gun was equipped with an open sight for distances up to 500m ; a telescopic sight , ( ZF 1х11 from the 3 . 7 cm Pak 36 anti - tank gun ) , could also be fitted . The recoil system consisted of a hydraulic recoil buffer and spring - driven recuperator . The carriage was of the split trail type , with suspension . Wheels with rubber tires could be removed , making the gun significantly lower and therefore easier to conceal ; the process took 30 – 40 seconds . The guns ' construction allowed toolless dismantling to five pieces , the heaviest of which weighed 62 kg . Development and production history . The cone - bore principle was first patented in 1903 by a German designer , Karl Puff . In the 1920s and 1930s another German engineer , Gerlich , conducted experiments with coned - bore barrels which resulted in an experimental 7 mm anti - tank rifle with a muzzle velocity of 1 , 800 m / s . Based on these works , Mauser - Werke AG developed a 28 / 20 mm anti - tank weapon initially designated " Gerät 231 " or " MK . 8202 " in 1939 – 1940 . In June – July 1940 an experimental batch of 94 ( other sources say 30 ) pieces was given to the army for trials . They resulted in some modifications and in 1941 mass production of what became 2 . 8 cm schwere Panzerbüchse 41 started . One piece cost 4 , 520 Reichsmarks ( for the sake of comparison , one 5 cm Pak 38 gun cost 10 , 600 Reichsmarks ) . The last gun was built in 1943 ; the main reason for the discontinuance was the lack of tungsten for projectiles . Organization and employment . The sPzB 41 was used by some motorized divisions and by some Jäger ( light infantry ) , " Gebirgsjäger " ( mountain ) and " Fallschirmjäger " ( paratrooper ) units . Some guns were supplied to anti - tank and sapper units . The weapon was employed on the Eastern Front from the beginning of hostilities ( the " Wehrmacht " possessed 183 pieces on 1 June ) , until the end of the war and also saw combat in the North African Campaign and on the Western Front in 1944 – 45 . Short - range shots from a sPzB 41 could penetrate most World War II armour ; a lucky shot could even damage heavy tanks such as the KV - 1 and IS - 2 ( at least in one instance a projectile penetrated the lower front plate of the latter ) . Self - propelled mounts . The sPzb 41 was also mounted on several vehicles , such as cars , half - tracks and armored cars : Service . Squeeze bore guns saw only limited use in World War II . Manufacturing of such weapons was impossible without advanced technologies and high production standards . The only country except Germany to bring such weapons to mass production was Britain with the Littlejohn adaptor which , although not a gun in itself , used the same principle . An attempt by a Soviet design bureau headed by V . G . Grabin in 1940 , failed because of technological problems . In the US , reports about the sPzB 41 inspired a series of experiments with 28 / 20 barrels and taper bore adaptors for the 37 mm Gun M3 ; the work started in September 1941 and continued throughout the war , with no practical success . The sPzB 41 combined good anti - armor performance at short range and a high rate of fire with small , lightweight ( for anti - tank gun ) , dismantleable construction . However , it also had several shortcomings , such as : Some authors that criticize the sPzB 41 concentrate mainly on the short service life of its barrel . However , its chance of survival after 500 short - range shots was slim anyway . It should also be noted that high - velocity guns with " normal " barrel construction also had a short service life , e . g . for the Soviet 57 - mm ZiS - 2 it was about 1 , 000 shots . In the end , the factor that brought production of the sPzB 41 to a halt was the shortage of tungsten . Ammunition . There were two shell types for the sPzB 41 : the armor - piercing " 2 . 8 cm Pzgr . 41 " and the fragmentation " 2 . 8 cm Sprg . 41 " . The Pzgr . 41 had a tungsten carbide core , a softer steel casing and a magnesium alloy ballistic cap . The core was 40 mm long and 10 . 9 mm in diameter and contained about 9 . 1 % of tungsten .