Hey Mike,
In all honesty I’m just repeating the info. that was passed on from the
seller. I really have no way of knowing if he measured them with a
choke gauge or not. The Parker letter did “not” specify anything in
regards to the chokes. Is there a quick and dirty way of making this
measurement without a choke gauge?

The bar type gauges are almost always inaccurate, sometime by quite a bit. The only way I know to acurately measure them is with a bore gauge. First you measure the diamer of the bore and then the diameter of the muzzle and subract.

Best,

Mike

Is the bore measured just ahead of the forcing cones?

For the purpose of measuring choke I use the diameter right before the bore starts tapering toward the muzzle, usually within 4" of the muzzle.

I have some vague idea that for English proof laws bore is measured at 9" from the chambers.

Best,

Mike