Nitrox

Well the 577REWA is a necked down .600NE. The bullet weight is 750 grains - the same as the .577NE 3". It is believed that the velocity of the orginal loading with 110 grains of cordite was 100 fps higher than the regular .577NE 3", which means the .577REWA is propelling the bullet of 750grains at 2150 fps.

Capacity vice the .577REWA case is on par with the .577 Tyrannosaur case ( both Horneber made, 216grain water capacity ), so you can expect to also reach 2400 fps without to many problems. I doubt that the Woodleight bullets ( soft point ) will hold up into game at that speed, so I keep the velocity at 2150 fps. This is reached with 165 grains of Hodgdon H4831 powder.
If you have further questions come back and ask.
Robert