The 6x45mm (6mm-223)

By Chuck Hawks

This wildcat is covered in some detail in "The 6mm as a Military Caliber," an article by Henry Song that can be found on the Naval, Aviation and Military History Page. Henry makes a pretty good case for the 6x45 (or 6mm-223 as it is also known) as a replacement for the under powered 5.56mm NATO cartridge.

In fact, I believe that the 6x45mm originated as a result of U.S. Army tests conducted years ago. Even then experts realized the limitations of the 5.56mm NATO (.223 Remington) round as a man-stopper. Recent events in Afghanistan and Iraq have again spotlighted the inadequacy of the 5.56mm, but this time a whole new cartridge has been developed as a potential replacement in the form of the 6.8mm SPC.

The advantage of the 6x45mm is that only re-barreling would be required to convert present M-16 and M-4 rifles to the improved caliber. The 6.8mm SPC would require a whole new "upper." However, with its bigger case and larger diameter bullet, the 6.8mm SPC hits harder than the 6x45. Whether Congress will authorize any change remains to be seen, so for now this is all just speculation.

The 6x45 has been used as a benchrest cartridge, and also as a varmint and minimum recoil deer cartridge. Certainly it is superior to the big case .22s (.220 Swift or .223 WSSM) in the latter role, although clearly inferior to the very popular .243 Winchester in killing power.

The 6x45mm is based on the .223 Remington case necked-up to accept .243" diameter bullets. The neck angle and everything else remains the same, so case forming is simple. Case length is 1.760" and COL is 2.260".

The 26th Edition of the Hodgdon Data Manual covered the 6x45. H335 and BL-C(2) are the powders suggested for top performance. Remington 7 1/2 and CCI 450 primers are also recommended. The Hodgdon technicians used a 24" test barrel to develop their loads.

For the varmint hunter, 27.0 grains of BL-C(2) powder can drive a 75 grain bullet at a MV of 2726 fps at a chamber pressure of 42,500 CUP. A maximum load of 29.0 grains of the same powder gave a MV of 2832 fps at a MAP of 47,000 CUP.

For hunting small CXP2 game, a 90 grain bullet can be driven to a MV of 2523 fps by 25.0 grains of BL-C(2) powder, or a MV of 2744 fps by 27.0 grains of the same powder. These are not impressive numbers, but with maximum loads the 6x45 should be adequate for small deer and antelope out to perhaps 200 yards.

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Copyright 2005, 2013 by Chuck Hawks. All rights reserved.