6×45mm

6x45 mm
Type	Rifle
Place of origin	USA
Production history
Designed	1965
Specifications
Parent case	.223 Remington
Case type	Rimless, bottleneck
Bullet diameter	0.243 (6 mm)
Neck diameter	0.272 in (6.9 mm)
Shoulder diameter	0.354 in (9.0 mm)
Base diameter	0.376 in (9.6 mm)
Rim diameter	0.378 in (9.6 mm)
Case length	1.76 in (45 mm)
Primer type	Small rifle
Ballistic performance
Bullet mass/type Velocity Energy 75 gr (5 g) SP 2,700 ft/s (820 m/s) 1,214 ft⋅lbf (1,646 J) 80 gr (5 g) SP 2,650 ft/s (810 m/s) 1,248 ft⋅lbf (1,692 J) 90 gr (6 g) SP 2,540 ft/s (770 m/s) 1,300 ft⋅lbf (1,800 J) 100 gr (6 g) SP 2,400 ft/s (730 m/s) 1,279 ft⋅lbf (1,734 J)

The 6x45mm cartridge is the .223 Remington or 5.56x45mm NATO round necked up to 6 mm. It is a fine small game or varmint hunting round. It can be used in small bolt action or AR-15 type rifles. It was also tested by the US Army for a Squad Automatic Weapon.

Overview

The 6x45mm has a rather small powder capacity and will thus give best results using bullets of low to moderate weight (up to approx. 90-grain (5.8 g)). Initial velocities are normally between 2,500 and 2,800 ft/s (760 and 850 m/s) depending on bullet weight. Due to the low velocity and moderate effect on the game, it is a rather popular wildcat cartridge for small game hunting for meat.

In 1973 the cartridge set a new IBS 200 yards (180 m) record of 0.3062 inches (7.78 mm). The cartridge could not compete with the .308 Winchester in match competition though and in the benchrest arena it was replaced by the 6 mm PPC. Today in the US this cartridge is relegated to the occasional varminter.

This cartridge has become quite popular in South Africa as a small game cartridge in bushveld conditions using the 100-grain (6.5 g) bullet at about 2,350 ft/s (720 m/s). At this velocity it is adequate for the most common small antelope - the impala, but it is also capable of handling slightly larger animals such as blesbok and in a pinch Hartbeest or Njala.

Ideal is regarded as around 2,300 to 2,400 ft/s (700 to 730 m/s). At this velocity meat damage is minimised, penetration is excellent, it has sufficient range for bushveld hunting (most shots below 150 yards (140 m)) and one gets reliable performance from conventional construction bullets.

The beauty of this cartridge is that you can build very small light rifles on the mini actions. It also has notably less muzzle blast than many of the “standard” calibres (.243 Winchester, .308 etc.)

The cartridge is not just short; it has a small case-head meaning you actually use the small bolt, not just a short action with a standard diameter bolt.

There is probably no other 'wildcat', which has seen as wide application as this one in [[Africa]] and it grew to such an extent that one large ammunition manufacturers started producing factory ammunition for it. This expanded its use to non-reloaders and increased its popularity further.

With the lighter bullets the cartridge can be used as a plains country springbok calibre if shots are kept below 300 yards (270 m).

Rifle availability

Rifles for this calibre are either built on the mini actions or alternatively people simply buy a .223 and rebarrel it. In addition to small bolt action rifles numerous companies in the United States are using the 6X45 on military and civilian semi-automatic rifles such as the AR15/M16. With so much surplus brass as well as the readily available .243 (6mm) bullets reloaders have multitudes of options when working up a load as well as commercially available ammo at prices equal to the .223/5.56.

Manufacturers of the rifles include companies such as The Spirit Gun MFG. Co, Cooper Firearms, and Les Baer. Ammunition is also readily available through many retail outlets and distributors, Black Hills Ammunition produces 6X45 ammunition.

Military

From a military application the 6X45 has not only downrange benefits; but substantial cost savings on the actual rifle hardware. The only change to the existing US military M4, M5, & M16 would be a barrel change. The case is the same as the 5.56 NATO and the OAL case length is the same as a 77 grain 5.56. Using the same magazine makes the 6X45 a viable contender for special security missions.

Downrange ballistics roughly increase 20% at the muzzle when comparing 77 grain VS the 100 grain bullet and this number jumps about 10% per hundred yards. When shot out of the tradition M4 carbine the 6X45 can provide infantry with long range capabilities while not being selected as a primary sniper in a platoon. The 6X45 died many years ago as a bench rest cartridge but with advances in powders and weapons platforms the cartridge has been reborn as a viable hunting round.

See also

• List of rifle cartridges
• 6 mm caliber
• Wildcat cartridge

References

• Sprit Gun Mfg
• Sportin Products
• Black Hills Ammunition
• Les Baer Arms