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Belgian bore diameter in millimetres

Belgian (Liège) proof marks · 1810 to today.
What it looks like
A decimal number such as 18.0 stamped on the barrel.
Where it is on the gun
Barrel.
Date range
1810 to today.

What it tells you

What this mark authorises you to say

The bore diameter. Before 1894 it was stamped in graduations of 0.02 mm; from 1894 the graduations became 0.1 mm. That change is itself a dating tool: a barrel marked 18.4 tells you the gun was proved before 1894, and one marked 18.4 in 0.1 mm steps does not exist.

What it does not tell you

What this mark does NOT say

It is the bore, measured at proof, and not the chamber, the calibre or the cartridge. It also describes the barrel as it was proved, and a century of wear, honing or reboring moves the number.

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 belgian (liège) 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.