How is choke designated?
There is no set measurement for choke. It is only relative to the bore size of the gun. There is a fairly wide tolerance that the diameter of a bore can be, and still be known nominally as that bore size. For example, 12 bore can be anywhere between 0.710 and 0.752. but the precise measurement that 12 bore should be is 0.729. In manufacture it is very often the case that guns will be turned out to finished size with slight variations either side of this standard, which is perfectly acceptable, and is why there are tolerances. However, let us imagine that a gun in question is exactly 729 bore diameter. On this basis a straight parallel tube out to the muzzle would be known as true cylinder. Improved cylinder would have a restriction over the bore size by 0.005 choke would have a restriction over the bore of 0.010 choke would have a restriction over the bore of 0.020 choke would have a restriction over the bore of 0.030 And full choke will have a restriction over bore size of 0.040 These
