Mark, for what it's worth, I messaged the following on determining chokes to Dave Miles yesterday on the Parker site:
"I'm trying to get my synapses in line, Dave, to remember where I read about .650 bores in older 16 gauges. My gunsmith felt there wasn't sufficient thickness to open my F/F 1914 Sauer to C/IC. Turned out those bores were .650 and the Sauer now paterns perfect C/IC.
"I erred in my message at midnight last night by confusing the circumstances of the too-tight Sauer with what I thought were the chokes of my 16 gauge hammer 0 frame 1889 Parker, and the PGCA letter confirming what it is: C/F not M/F.
"I refuse on principle to put the error down to old age! It shows, however, that the determinative of choke is the patterning board. (Note JOC's Shotgun Book provides 16 gauge Inner Bore Diameters of .665, .673 and .664 of Browning, Remington and Winchester respectively.)"
