|Place of origin||Sweden|
|No. built||Prototype only|
|Parent case||.22 WMR|
The 4.5mm MKR cartridge was a prototype Swedish rifle cartridge.
The 4.5mm MKR was originally developed by Interdynamic AB, a Swedish company, in the 1980s, right around the time of the rise of "micro-caliber" popularity, when firearms companies everywhere were trying to achieve a type of practical and cheap ammunition. Micro-caliber (less than 5mm or .20 caliber) ammunition makers wished to achieve high velocity, flat trajectory and good penetration in automatic weapons, and with low recoil. The tiny size of the bullet required only a simple blowback autoloading system rather than a more complex design. The lightweight bullet, 1.58 grams (24.4 grains), achieved a muzzle velocity of about 3,270 feet per second. The effectiveness of this bullet was claimed to be on par with a 5.56×45mm NATO bullet up to 300 meters.
Due to concerns about stopping power, reliability, and problems with using rimfire ammunition, the MKR project was abandoned at the prototype stage. The 4.5mm MKR never saw service or any kind of widespread use.
The 4.5mm MKR was essentially a .22 WMR necked down to a 4.5mm bullet, designed to be used in the Interdynamics MKR rifle. The Interdynamics cartridge featured a curved taper and a 4.5mm caliber pointed bullet, made of solid, cold swaged copper.
- Bullet width: 4.5mm (.177 in)
- Bullet weight: 1.58 g (24.4 gr)
- Muzzle velocity: 1,000 m/s (3,270 ft/s)
- Muzzle energy: 790 J (583 ft lbs)
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