If you look at the British proof house charts they list 16 gas as .662". "IF" you look up the weight of lead & calculate the diameter you will find that every gauge in the British system is "Just a Wee Bit Off". Calculations based on the weight of lead gives a very slightly larger diam than the charts. My "Assumption" is they took some given weight of pure lead, quite possibly a pound, formed it into a sphere & measured the diameter & calculated the rest. Perhaps in forming the sphere they compressed the lead just a bit & then used this size as the basis for the rest. By mathematical calculations .662" for the 16ga "Fits" in with all other gauge sizes from 1 to 172.28 in both English & German charts. Call it what you will, but if .662" is incorrect then ALL other charted gauge diameters are also incorrect.
One thing is for certain, Gunmakers have not always adhered to the standard. As noted for many years L C Smith bored 16 gauge barrels to "Their" standard of .650", others have also varied. None of this affects the true standard based on that 16 pure lead balls with a diameter which just fits the bore weigh 1 pound. Off size balls do not fit that standard.
