The 585 Nyati can be considered the most powerful round chambered for a shoulder fired rifle. Before you start to correct me on the .50 BMG being more powerful (and you are right) it is not generally considered an offhand shoulder fired cartridge.
Here you see it compared to the 30-30 Winchester
The 585 Nyati generates 10,600 ft lbs of energy with a 750gr bullet traveling at 2525 fps. The cartridge was developed by Ross Seyfried and is based off the 577 Nitro cases. The reason behind the cartridge is to have a very powerful round that can be chambered in bolt action rifles for the budget minded. Generally such a powerful round was in the realm of British double rifles which are very expensive and thus limits who may be able to take advantage of such a round on a dangerous hunt.
The rifles chambered in such a cartridge weigh in at approximately 10 pounds. With full power loads and a quality muzzle brake the cartridge generates 150 ft lbs of energy, compared to a 30-06 with a full power load generating 20 ft lbs of recoil energy. One would greatly benefit from a well made recoil pad and a high tolerance for pain if you plan to shoot this often, or be into that sort of thing (no judgment).
Nyati translates to Cape Buffalo in many African dialects such as Swahili. Which is fitting as this cartridge’s purposes is for hunting tough and dangerous game.