The 6x45mm, also known as the 6mm-222 Remington, is a wildcat cartridge created by necking up the .223 Remington (5.56x45mm NATO) case to accept a 6mm bullet. The intent behind this modification is to offer improved performance for hunting and target shooting by enabling the use of heavier, higher ballistic coefficient bullets, which can provide greater accuracy and energy on target.
Typical bullet weights for the 6x45mm range from 55 to 87 grains, making it suitable for small to medium-sized game such as varmints, deer, and antelope. The cartridge is appreciated for its versatility, mild recoil, and the ease with which it can be adapted for use in rifles chambered for .223 Remington, requiring only a barrel change.
Its performance generally offers a good balance between speed and terminal performance, making the 6x45mm a popular choice among handloaders and custom rifle enthusiasts aiming for efficient, flat-shooting rounds for precision applications.
Due to its wildcat status, factory ammunition for the 6x45mm is not widely available, so handloading is typically necessary.