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British proof — crown over SP

British proof marks · 1925 to today; used alongside the definitive mark before 1954, and as a definitive mark in its own right after it.
What it looks like
A crown with the letters SP beneath it.
Where it is on the gun
Barrel flats.
Date range
1925 to today; used alongside the definitive mark before 1954, and as a definitive mark in its own right after it.

What it tells you

What this mark authorises you to say

Special proof: the barrel was proved with heavier loads than the standard test requires. On a gun built for magnum cartridges or for a heavy game load this is the mark that says so.

What it does not tell you

What this mark does NOT say

It only means heavier than the standard of the day. An SP proof from 1930 is not equivalent to a modern magnum proof, and the pressures involved are a century apart.

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.

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 british proof marks

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.