I have used a 50 cal white rifle for years with a 600 gr lead bullet. Though I try and keep my shoots under 300 yds I have taken two elk one at 365 yds a one at 335yds.
If you have a good range finder, a quick ajustable receiver sight such as a lyman and good vision you can drop game at 400 yds. You must go out and practice shooting from your range finder. Not marked yardage. i watched a good freind, who was killed in a plane crash last year, take a mule deer a few years ago at 425 yards. he ranged it I ranged it and then he layed his white over the front rack of his quad and POWWWW !!! blew a hole right through it and left a 4 foot rooster tail in the dirt behind it. The front sight insert you use is important for long range.
It can be done with practice before the hunt.