Home / Proof Marks / "Fluss Stahl Krupp Essen"

"Fluss Stahl Krupp Essen"

Barrel steel markings · About 1890 to the 1930s.
What it looks like
The words FLUSS STAHL KRUPP ESSEN, or the English form FLUID STEEL KRUPP ESSEN, stamped along the top rib of a double.
Where it is on the gun
Top rib, between the barrels, or the barrel flat.
Date range
About 1890 to the 1930s.

What it tells you

What this mark authorises you to say

The barrel steel is fluid steel made by Krupp of Essen, and it is a step up from the entry-grade names. Steel names were grade indicators and they were ranked: Smokeless Powder Steel and Nitro Steel at the bottom, the continental mid-grades such as Cockerill, Siemens-Martin and Wittener Excelsior above those, Krupp Essen a step above that, and Vickers and Nickel Steel higher still. On a gun whose grade stamp has worn away, the name on the rib is what remains of the gun’s original grade and era.

What it does not tell you

What this mark does NOT say

It does not certify the barrel as safe. This is the specific error the mark invites: a name stamped on the rib in 1910 says the barrel was made of good steel for its time, and nothing whatever about what may be fired through it a century later. "Krupp" describes the material, not a test result.

Sources for this page

Every claim above is attributed. The class of source is shown with each one, because a national proof house and an anonymous forum table are not the same evidence — and on proof marks the difference matters.

Related on this site

Makers whose guns carry marks like this:

Reading marks to identify and date a gun

Proof marks name the test and the era. The serial number, where a maker published a browsable chart, can name the year. The lookup cites the threshold behind every result.

Open the serial number lookup

Other barrel steel markings

Mark descriptions observed and verified 2026-10-14. Proof marks are stamped by hand on guns up to a century old; a photographed stamp and a description in a book are not the same evidence. If a mark on your gun does not match anything here, that is a real answer — see the notes on unidentified marks.