Can anyone explain this marking on my 1940-41 Webley Mk. IV .38?

[Boy Howdy]

Why is it marked .38 145/200 instead of 38/200?

  200?

[dcollector]

The numbers 145/200 refer to the range of weight of the bullets (projectiles) that are suitable in this revolver. 

U.S. Commercial loadings use 145/146 grain bullets. 

The original British loading, adopted in 1932, used a 200 grain lead bullet. Under pressure from the Geneva Convention in 1938, the bullet was changed to a 173 grain jacketed bullet.

.38-200 is a cartridge developed by .38 S&W in 1877

[Boy Howdy]

Thank you dcollector.