Current Rifle Cartridges
6x45mm for AR-15
This cartridge was introduced by Black Hills  Ammunition Company in 2010 for use in AR15 / M16 rifles.  
The cartridge is produced by taking a .223" caliber case and necking it out to accept larger 6mm or .243"
It is similar to the 6mm TCU, except it is not fire formed and may have a slightly different neck angle.   
The AR-15/M16 rifle can easily be converted to the 6×45mm with a simple barrel swap with few or no further
modifications to the rifle.
The samples available below were produced by COR-BON using Lapua Match .223 cases.
Please note in the top
right picture for size
comparsion, left is larger
diameter 6mm projectile
and right is smaller
diameter .223 projectile.