20x138 Solothurn


#1

Who made this 20x138 Long Solothurn and what kind of projectile does it have?
20/40 at 12oclock
T at 3oclock
41 at 6oclock
E12 at 7-8oclock at a 45degree angle
Circle with 2 arrows crossed over the circle at 9oclock.
Has a Blue projectile and white band above case mouth.
Thanks,
Bob Ruebel


#2
  • I don’t know about the 20mm projectile but the 20X138B Long-Solothurn belted case was made in 1941 in FINLAND at Tikkakoski arsenal. I have a similar 20X138B fired brass case headstamped “E4”, circle with 2 crossed arrows, “20/40”, “T” and “41”. I posted the headstamp photo here on the new IAA forum a few months ago but NOBODY has an answer for me. I’m interested in the meaning of all the headstamp markings [excepting “T” and “41”]. I know that there are also ammo collectors in Finland but I cannot understand why they have no answer. I’m not asking info about the dark side of the Moon. Liviu 03/17/07

#3

I will answer this next week when I get new info ;)


#4

A blue projectile is typical of AP made in Finland. You can see one attached to the 20x113 Lahti L34 in this photo:


#5

To be correct the projectile is an AP-T.
Blue in Finland stands for AP and the white ring is indicating the tracer.

The caliber is correctly designated as 20x138B Rheinmetall.


#6
  • Well, what about the headstamp markings??? What is the meaning of “E4” [or “E12”], circle with 2 crossed arrows and “20/40”??? Liviu 03/17/07

#7

[quote=“EOD”]To be correct the projectile is an AP-T.
Blue in Finland stands for AP and the white ring is indicating the tracer.

The caliber is correctly designated as 20x138B Rheinmetall.[/quote]

EOD insists on calling the long belted Solothurn a Rheinmetall. Checking with WOODIN LAB - he is correct. This caliber was designed by RM and widely used by Germany in AA guns but is best known in the US for its association with the Solothurn AT guns many of which were imported and sold to the public during the 50s and 60s. The Finnish Lahtis which were imported during the same period were mostly chambered for this caliber as well.

GERMAN AA GUNNERS LOADING MAGAZINES FOR 20MM AA GUNS


#8

Solothurn was used by Rheinmetall as the Swiss base for developing armaments prohibited to Germany by the Treaty of Versailles. I’m not sure whether or not Rheinmetall owned Solothurn, but they were certainly closely allied, and once Germany decided to ignore the restrictions Solothurn developments became Rheinmetall ones.

So the 20x138B round is known as the “Long Solothurn” because that’s where it was developed, in various cannon which led to the Rheinmetall Flak 30 and KwK 30.


#9

In a recent article (July 2006) J.B. Anderhub wrote in the German ECRA bulletin, he described the background of this cartridge. Everyone interested should try to get a copy.
In his Article Anderhub is giving the following info.

  • According to the Allied postwar “Unterluess Report No 38” (compiled by German military industry engineers) the development of the German Flak 30 in 20x138B was carried out in about 1927-1929 amd the gun was tested by the German Navy in 1930/31 (and adopted as Model of 1930).
  • “Waffenfabrik Solothurn” was founded on June 27 in 1929
    And from another article (other autor) on German Arms export to Russia:
  • Rheinmetall exported the first 20x138B AA-guns to Russia in 1930

Now everybody can figure himself if Waffenfabrik Solothurn was able to develop a weapon system within six months AND can contradict the given report info.


#10

Thanks, that’s helpful information. It has prompted me to turn to Musgrave’s ‘German Machine Guns’, which describes the relationship between Rheinmetall and Solothurn in detail. Rheinmetall actually set up Solothurn as its Swiss subsidiary in 1929, in order to develop new and improved weapons.

According to Musgrave, the Flak 30’s immediate ancestor was originally known as the ST 5 (later ST 52), and development was started by Rheinmetall in the late 1920s, as the Unterluss report says. The project was then transferred to Solothurn, where it became known as the S5-100 series. There it was further developed with an improved version, the S5-106, being demonstrated in 1933 (a couple of these were bought by the USA for evaluation in 1937/8). There was also the T5-150, which became the KwK 30, using the same ammo.

Musgrave is good on narrative but light on data, which can be frustrating. For instance he says that the ST 5 “was simply a continuation of the 20mm Ehrhardt cannon” from WW1, which did of course use a much less powerful 20x70RB cartridge. He says that the S5-100 series did use the 20x138B, “which later became standard for the German 2cm Flak”. At what point the changover in cartridge occurred is not clear in his book (nor how the development of the 20x138B relates to that of the 20x105B “Short Solothurn”, also used in automatic cannon as well as the S18-100 series anti-tank rifles).

An interesting subject…


#11

Yes, some relations still have to be cleared up.
This actually reminds me on the 20x77B I think which may be also some sort of link and predecessor of/to the 20x138B (and 20x105B). I wish we had the files…


#12

[quote=“EOD”]Yes, some relations still have to be cleared up.
This actually reminds me on the 20x77B I think which may be also some sort of link and predecessor of/to the 20x138B (and 20x105B). I wish we had the files…[/quote]

Now, what do we have to call the 20mm SHORT Solothurn? This is also mostly known in the US as being chambered in the first model of the SOLOTHURN AT gun. Only a few of these came here but more Hungarian base fuzed APHEs in this caliber have shown up in the US than one would expect.


#13

It is a Rheinmetall and Polte thing according to Anderhub but the exact details are still to be found out.


#14

[quote=“EOD”]Yes, some relations still have to be cleared up.
This actually reminds me on the 20x77B I think which may be also some sort of link and predecessor of/to the 20x138B (and 20x105B). I wish we had the files…[/quote]
I have a copy of a factory drawing of that round, dated 28/10/1935. It has a more slender case than the 20x105B, with a rim and body diameters of only 23mm - it has only a slight bottleneck. If that was the date of the design, it’s hard to see what it was intended for.


#15

AP-T 150g
20/40 = 20mm case model of 1940
T = Tikkakoski
41 = 1941
Circle with 2 arrows crossed over the circle = acceptance stamp
E12 = delivery lot


#16

[quote=“Tony Williams”][quote=“EOD”]Yes, some relations still have to be cleared up.
This actually reminds me on the 20x77B I think which may be also some sort of link and predecessor of/to the 20x138B (and 20x105B). I wish we had the files…[/quote]
I have a copy of a factory drawing of that round, dated 28/10/1935. It has a more slender case than the 20x105B, with a rim and body diameters of only 23mm - it has only a slight bottleneck. If that was the date of the design, it’s hard to see what it was intended for.[/quote]

1935 then if this date is representing the development time the cartridge then seems not to be a predecessor of the 20x138B.
Might it have been intended for aircraft guns?
Anyone else on that?