they are indeed millimeters - the larger number is the bore diameter (when proofed) and the smaller number is the choke diameter. multiply whose numbers by .03937 to convert to decimal inches. the easier to remember version is that a mm = 40 thousands of an inch - not exact but mighty close....so a tenth of a mm = 4 thousands. multiple the metric difference between bore and choke by 4 and you're there - in your case, 9 x 4 = 36, and 5 x 4 = 20.
belgian proofs also offer the weight of the barrel set when proofed, expressed as "0 kg 000"....whole kilograms first, with fractional kilogram following. kilogram = 2.2 pounds to convert. if you have accurate scales to weigh the barrels, their present weight may be compared to the proof - belgian rules state that a barrel set more than 3% lighter than marked is considered to be out of proof.
while i was writing this reply parabola had posted his response - the same thing, but coming from the opposite direction.
Last edited by graybeardtmm3; 11/21/25 02:26 PM. Reason: additional info
