20x70mmRB Becker


I got these 3 rounds, and have a problem asigning the calibre. Some call it 19mm, some 20mm. Which one? armorypub.com/2000/2-00.htm


Definately 20mm.


So would “20x70mm Becker” be an official way of expressing this calibre?


I pulled the projectile out of the 3rd round. Here is the base of the projectile. What is the symbol to the right of the crown? Also, the bottom of the projectile looks like a plunger going into the main body of the projectile. Was the cavity filled with something? The same symbols are present on the side of the projectile, also with “3” and “18”.


Vlad, this is a tracer, the small hole is the flame channel to ignite the tracer composition. Once the projectile left the barrel the base is blown out and a huge tracer will show the trajectory and maybe will set parts of the target aflame if something combustible is hit.


20x70RB (or RR) for rebated rim.


Yes and then we should also distinguish between type 1 and type 2.


I have 3 rounds, they all are from 1918, 1 is straight and 2 are bottlenecked. Why did they go from straight to bottlenecked? When was the change made?Which is more rare?


Type 1 = totally straight
Type 2 = slight bottleneck
Erhardt (and no Becker at all) = Bottleneck

Can you show us a side view?


Here they are.


Vlad, is the left one fired and the projectile (if you try to seat it there) is loose? Then the neck as we can still see it on the two other cases got straigtened out by the firing process.
If so all three should be Becker Type 2.


Yes, yes, yes & yes. You are correct. What is Erhardt?


The 20mm Ehrhardt (note the spelling - it’s easy to get wrong!) was an entirely different design of automatic gun from the Becker, using a short-recoil mechanism rather than an API blowback. It was the progenitor of the Solothurn/Rheinmetall series of cannon used in WW2, just as the Becker was the progenitor of the Oerlikon series.

Despite this difference, it uses ammunition which was presumably based on the Becker’s as it is remarkably similar. The cartridge case is the same length, has a slight bottleneck and also features a rebated rim (although, unlike with the Becker, this is not necessary for the gun to work). The main ID point is that in the Becker, the junction between the extractor groove and the body of the case is rounded, but in the Ehrhardt it is sharper (see the pic below from the Ammo Photo Gallery on my website).

The Ehrhardt was put into production at the end of WW1 but it seems it was too late to get into service. I have examined one with serial number 51, so there were presumably at least this many made.

19-20mm experimental cartridges group: 19x114R (WW1 Szakats), 20x110 (for scale), 20x72RB(E) (WW1 Ehrhardt), 20x120RB Simonetta (1930s), 20x135 Polte (German pre-WW2: replica), 20x138RB (German WW2 unknown: replica), 20x122 case (post-WW2 French AA 5CG series), 20x126B (post-WW2 French AA 5CG series - used German projectiles), 20X158RB (US T5, for post-WW2 T33 aircraft gun)


Tony, yes you are right of course with the Ehrhardt. Thanks for pointing it out.