4.5 mm mkr

The 4.5 mm mkr cartridge was developed by Interdynamics AB, a Swedish company, in the 80s. It was essentially a .22 WMR necked down to a 4.5 mm bullet, designed to be used in the MKR rifle.

Due to concerns about stopping power and problems with using rimfire ammunition the MKR project was abandoned at the prototype stage and thus the 4.5 mm mkr never saw service or any kind of widespread use.

Specifications
Bullet width:     4.5 mm (.177 in) Bullet weight:    1.58 g (24.4 gr) Muzzle velocity:  1,000 m/s (3,270 ft/s)