How long did the 5 cannelure guard production last? How many months?
From HWS Vol 1 (p. 177):
The five cannelure case was adopted in January 1908. In late 1909 (no month given) prison guards complained that the cases ruptured at the grooves when fired and in March 1910 the cannelures were replaced with six short longitudinal flutes.
So, If my math is correct, that is 26 months.