Interesting article from 2004
This is another wildcat come good here in Africa.
The 6x45 is a wildcat created by necking up the 223 Remington to 6mm (.243). This wildcat first appeared in 1965 shortly after Remington launched the 223 as a sporting cartridge. Initially it was quite popular as a benchrest and varmint calibre in the US (varminters liked the reduced winddrift as opposed to the 22 calibres). The cartridge will launch 70 and 75gr bullets at 3000ft/s and the 100 gr bullet at 2400ft/s. The cartridge was also quite popular in NRA match competitions.
In 1973 the cartridge set a new IBS 200yard record of 0.3062”. The cartridge could not compete with the 308 Win in match competition though and in the benchrest arena it was replaced by the 6mm 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, mainly I believe because our local gun magazine has written some glowing eulogies to it. In essence in the SA application, it is used as a small game bushveld cartridge with the 100gr bullet at about 2350ft/s. At this velocity it is adequate for our 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.
A little aside here: A "bushveld calibre" is a calibre that throws a bullet at low velocity. Ideal is regarded as around 2300 to 2400ft/s. At this velocity meat damage is minimised, penetration is excellent, it has sufficient range for bushveld hunting (most shots below 150 yards) 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 (the Zastava mini action has been the action of choice). Many people have fallen in love with these small “sexy” rifles and the 6X45 with its low recoil is perfect for this application. It also has notably less muzzle blast than many of the “standard” calibres (243, 308 etc.)
Note, 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 of our larger 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.
Many people obtained these rifles under the pretext that it is for the wife or children (and the rifle is truly excellent for this purpose) and then fall in love with it and before long it is their preferred rifle.
Rifles for this calibre are either built on the mini actions or alternatively people simply buy a 223 and rebarrel it. People who fall in love with small rifles such as .22 Hornets etc. will understand the magic of this little cartridge.
Give me a little longer, I will probably come up with a bunch of other dubious reasons....bottom line I think it would be something different and a bit of fun with the promise of a very accurate rifle. 
