20mm - Becker or Erhard?

[US-Subs]

I have several 20mm Becker, with variations in the cases on some. This one is more significant, however, a more prominent bottleneck and slightly wider case. The rim is 20.9mm vs 20mm on one of my Becker. I can find very little information on the Erhard, can anyone assist?

 

[rigby]

You definitely have a 20mm Erhardt cartridge.
So far, I have only seen this type of head stamp on Erhardt cases.

 

[Tony Williams]

From my forthcoming book Autocannon: a History of Automatic Cannon and their Ammunition:

2CM ERHARDT FLZK: 20 × 70RB (E) AMMUNITION.

The Erhardt FlzK (Flugzeugkanone, or aircraft cannon) was a Rheinmetall development which fired a 20 × 70RB cartridge (very similar to the Type 2 Becker’s and often mistaken for it). It employed a scaled-up version of the Dreyse short- recoil design, introduced in 1912 in an infantry machine gun of that name. This used a pivoting block lock designed by Louis Schmeisser, a famous gun designer who ironically is best remembered in the popular name of a sub-machine gun with which he was not in fact involved. His mechanism has the bolt supported by a locking piece that pivots downwards under the control of cams in the receiver, releasing the bolt to continue rearwards.


The Erhardt weighed 36kg, had an L/50 barrel and fired at 250–300rpm from a side-mounted box magazine. The locked-breech mechanism was considered superior to the Becker’s by the APK (Artillerie Prüfungs Kommission = Artillery Test Commission) but it did produce more recoil and vibration, which led to many stoppages.


The Erhardt did make it into production and at least fifty-one were built (one surviving example is stamped ‘51’), but it appears to have been too late to see service. After successful efforts to conceal it from the Inter-Allied Control Commission – the Allies apparently learned of its existence but were unable to locate any guns – the design was further developed in the 1920s into the ST-5 and then ST-52 before further development was (at least nominally) transferred to Solothurn.

 

[MINENAZ16]

What is the filling of the shell ?

 

[Tony Williams]

This is all I have on the ammo (also from the book):

20 × 70RB ERHARDT


This is for the German Erhardt FlzK (Flugzeugkanone, or aircraft cannon) which entered production by the end of World War I but did not make it into service.


The brass cartridge case has a slight bottleneck and a rebated rim, and is often confused with the Becker Type 2, but the base and rim are different, about 1mm more in diameter and with a less- rounded base.
Overall length of the complete round is 143mm and the weight is 193g. Details of the loadings are not known, but projectiles were the same as used in the Becker rounds and a muzzle velocity of 670m/s
has been quoted.

This cartridge was also apparently selected for the experimental Scotti M35 aircraft gun of the mid-1930s. The Erhardt was the ancestor of the Rheinmetall/Solothurn 20mm cannon developed through the 1930s.