Could not find anything on it.
I found this on ammo-guide (though i let me subscription lapse after i found lots of the diagrams were off in angles and some measurements.
its more-so written and intended as a DGR not a LR caliber
Invented by Jeff 'jeffeosso' Smith of http://accuratereloading.com/
- the .500 Accurate Reloading is intended as the minimum .510" DGR (dangerous game rifle) cartridge. This is a shortened and improved .416 Rigby/.338 Lapua Magnum, necked to .510" to approximately 130 grains of water capacity.
Designed on 2/19/06 and revised on 2/1/07, the first working rifle is being built on an Enfield 1917, Winchester Bauska .510 24" barrel, 1:15 twist. It is designed to propel the 535 gr. bullet to 2350+ fps or the 600 gr bullet to 2150+ fps, matching the .500 Nitro Express/.500 Jeffery in a bolt gun.
While .500 Accurate Reloading operates at a higher pressure than the .500 Jeffery, it is not designed for high velocities like many other wildcats. The shorter length allows this round to be built into many standard length sporter rifles