Larry,
Maybe it's me but I understood perfectly well what Rabbit was saying.The brass choke gauges are only any good and then only as guidance if your bore is 0.729" for a 12.
In case there is any more confusion to be cleared up, a brass gauge calibrated to suit 0.729" is not any good for overbored 12,s or standard bore 20's.
Just in case it is not clear.
Finally being sensical, you need to measure a barrel with a bore gauge such as a Chubb dial gauge. But no matter what the constriction is at the muzzle, that is NOT the choke.It is the constriction.
Choke is the percentage of pellets of the complete number of pellets loaded into the cartridge that are within a 30" diameter circle drawn around the main mass that have hit a pattern board or pattern plate when shot at a distance of 40 yards from the plate.
Measured constriction of choke will only give an approximate idea of what pattern to expect. This can be greatly influenced by various cartridges and the construction of cartridges with regard to powder, wad, shot etc.
