What's the original spec's on barrels???

[John Sabato]

GT, the largest bore on a marked original barrel I have ever seen is 8.85.. but the specs in my diagram above allow for as high as 8.86mm

8.85 = 0.3540 inches
8.86 = 0.3544 inches

The lowest I have ever seen is 8.82mm and this is also the low end of the specs above and calculates to 0.3528 inches on the low end.

".357" caliber converts to 9.067799999999998 mm

and .356 converts to 9.042399999999998

...both of which are out of spec according to the original 1913 blueprint that I have posted the extract from... but the question here is: Does the American .357 caliber refer to the land or groove diameter?

The land diameter of the 1913 blueprints is 9.1mm and that converts to 0.364 inches...