This is going to sound argumentative, but that is not my motive at all so apologies in advance. I just tried it in my lounge-room with the .577 x 2 3/4 and my .500/.450 x 3 1/2, and no way do those empties fall out until the barrels are at least 45 degrees, and to be reliable every time, closer to 70 or 80 degrees.

Perhaps this is cartridge dependent, because "very little elevation past the horizontal' and "very slightly muzzle-high" certainly don't result in case extraction in my non-ejector guns.