Would just like to add a note of caution about British cartridges.
In the photograph are two cartridge cases from boxes of cartridges sold for guns with chamber lengths of 2 1/2 inch one is 67mm and the other is 65mm, you can see from the shredded top that the 67mm has entered the forcing cone causing an increase in the guns recoil. So some guns with 2 1/2 inch chambers are very sensitive to the cartridge length used.