Home / Proof Marks / "Whitworth Fluid Compressed Steel"

"Whitworth Fluid Compressed Steel"

Barrel steel markings · About 1874 to the 1920s.
What it looks like
The words WHITWORTH FLUID COMPRESSED STEEL stamped along the rib.
Where it is on the gun
Top rib.
Date range
About 1874 to the 1920s.

What it tells you

What this mark authorises you to say

The top of the barrel-steel hierarchy. Sir Joseph Whitworth’s adaptation of Bessemer’s principle of hydraulic pressure casting was patented in 1874, and its advantage was uniformity — the absence of the inclusions and laminations that plague forge-welded barrels. Whitworth steel was reserved for the highest-grade guns, so the marking is as much a statement about the gun’s grade as about its metal.

What it does not tell you

What this mark does NOT say

It does not make the gun safe with modern loads, and it does not guarantee the barrel is original — rib markings on restocked or rebarrelled guns are sometimes not what they seem. A Whitworth barrel from 1895 is an excellent barrel of 1895.

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.