I saw a reference to the barrel of the 220mm L Mle 1917 Schneider gun being treated with autofrettage in GBM and wondered how many other
WW1 artillery pieces had their barrels made from steel tube which had been autofrettaged - anyone know?
For the uninitiated autofrettage is a process where a steel tube is filled with hydraulic fluid and the pressure of the fluid is increased until the
inner part of the tube exceeds the elastic limit of the steel but the outer part does not. The effect is to create a zone in the steel where there
is a permanent inward directed stress in the steel. The resists cracking and makes the steel capable of handling higher internal pressures
than untreated steel. For a gun barrel an autofrettaged barrel can be much lighter and thinner than an untreated barrel.
As an example a 240mm Mle 1903 coastal defence gun had an L/26 barrel which weighed 14.6 tons and a range of about 12.5km - this had to be an untreated barrel because the
process was invented by the French engineer Jacob in 1907. The 220mm Schneider gun had an L/35 autofrettaged barrel which weighed 9.3 tons and had a range of 22.5 km.
