Gunner500,
Saw in the thread above that you plan to shoot Nilgai in Texas.
Of the Nilgai I Have shot here, both have been taken at less that 100 yards. It appears to be a matter of cover.
In wide open range they can see you hundreds of yards away, but in thicker cover, you can get much, much closer. Late this spring, I shot this one at less than 20 yards with my .405 double rifle:
BTW, this was in south Texas at Hondo west of San Antonio. Where in SE Texas can you hunt Nilgai?