With only .006" taper in the case, it is virtually an Improved ctg. from the get-go. However the neck is much longer than needed.
The case capacity, holding 77gr. of rifle powder and a 340gr.(about) bullet was a decent load for it's use.

The 11mm Mauser was a black-powder cartridge developed for the Mauser Model 1871 rifle, and used later in the 71/84 variant.
It is no longer in production, however it is available from custom loaders and handloading can be done to replenish spent ammunition.

Case length: 6 cm
Bullet diameter: .446 in (11.3 mm)
Rim diameter: .586 in (14.9 mm)
Base diameter: .516 in (13.1 mm)
Neck diameter: .465 in (11.8 mm)
Shoulder diameter: .510 in (13.0 mm)
Used by: Germany, Japan, Qing Dynasty, Uruguay, Korean Empire