Home / Proof Marks / London — crown over GP

London — crown over GP

British proof marks · 1637 to today.
What it looks like
A crown with the letters GP beneath it.
Where it is on the gun
Barrel flats, breech and action.
Date range
1637 to today.

What it tells you

What this mark authorises you to say

Definitive London proof, and one of the oldest marks still in use anywhere: the London Proof House has been applying crown-over-GP since 1637, which makes it older than most of the guns it appears on by two centuries. On a British side-by-side the mark sits in a small archive of stamps on the barrel flats — crowns, letters, numbers, sometimes a fleur-de-lys — each recording a different part of the gun’s life. This one records the definitive test.

What it does not tell you

What this mark does NOT say

It does not record the date on its own, and it does not say what load the gun may be fed. The cartridge and pressure information lives in the separate marks beside it.

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.