Looks like I'm going to have to eat my hat again but the "16.3" and "16.4" seem to be a little larger or struck a little different. But the decimals for the diameter in inches is centered vertically. And from this example,
http://www.cabelas.com/cabelas/en/conten...erarchyId=11655 (choose the barrel flat pics) , the decimal is centered horizontally and vertically between the numbers. But the rhombus/diamond still puzzles me. Usually examples for the British are rotated 90° and the "c" is missing, unless during 1954-1989(as Terry L. posted) but with "Crown" over "BP"(black powder for 65 grains) instead of "BNP"(Nitro)? The following is a excerpt from an Appendices issued by the British Proof Authorities:
"At proof if a plug gauge of .729" diameter(but not one of .740") will enter the bore to a depth of 9in., that barrel is at present marked .729" and under the 1925 Rules of Proof would have been marked 12- and so on for the other bore sizes. The same system is used for the metric marks, but the tolerance has changed to 0.2 of a millimetre.
Rule 6 of Rules of Proof 1898 read as follows:
"If any Barrel of the First Class which shall be marked as proved under the Principal Act or these Rules, shall by any Process of Manufacture or by any other Means whatsoever other than the User and Wear and Tear thereof, be so enlarged in the bore that it will accept to a depth of 9" from its breech face, a plug gauge of the next larger diameter to that marked on the occassion of the last proof or reproof, and thereby be unduly reduced in substance and strength so as to become dangerous to the user, such barrel shall be deemed unproved. A Barrel enlarged in the bore by 0.2mm beyond the size marked shall be deemed to be unproved."
For now I still don't know why the inches & mm don't ghee-haw.
Kind Regards,
Raimey
rse