The D=6.5/19 is chamber dimensions. This would interpret to a 6.5 CM (65mm/2 9/16") chamber length having a diameter just ahead of the rim seat of 19mm (.748"). As I recall when two diameters are found on the same bbl as the 16.7 & 16.8 the smaller one was measured before final finishing of the bore with the larger on being final bore dia. Thus in final finishing it was enlarged from about .657 to.661". The choke remained constant at 16.3mm or .642", thus about .019" constriction.

Miller/TN
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