Despite the name this cartridge was invented by P.O. Ackley a prolific American wildcatter. Wildcat cartridges are ones that are not made to a standard adopted by any major manufacturer.
This particular cartridge could send a .22 caliber round 5,000 fps (1,524 m/s). The case it uses in this picture is that of a .378 Weatherby Magnum necked down to hold a .223 caliber bullet, but another design of the same name used .50 BMG cases.
Thats not what’s happening though. The Casing is a .378 case but the neck of the case (which holds the bullet in place) is formed down to .223. The barrel is also presumed to be .223 diameter with a chamber that is reamed out to accommodate the length and diameter of the cartridge to be fired. It’s a path to putting a ton of powder behind a small diameter bullet (much like an even more extreme version some more modern calibers like 6.5-300 weatherby magnum). Actually with a little work (and some very long and heavy .223 diameter bullets) you could probably make this thing hilariously accurate for a thousand rounds or so before you absolutely wrecked the rifling.
I agree. Every round would be hand loaded (because no company loads it). And precision is nothing more than repeatability. If you’ve found a good action and barrel nothing should stop you from shooting sub MOA groups.
For the most part particular chamberings are only more or less ‘accurate’ based on the ballistic coefficient / drop and the standard at which the manufacturer makes the cartridges.