I think being careful means that you know that you have a bullet that will penetrate through and make holes in vital organs from the angle and spot you have to shoot from.
A 270 with 130gr ballistic tips is pretty questionable shooting from a rear facing quartering angle, it might not penetrate through enough elk to reach the heart lungs. A 140gr Failsafe would as long as the shot isn't from 500yds away.
If you can't make a shot that will reach the vitals you shouldn't take the shot with any rifle from any range.
I haven't seen as many Elk killed as some on this forum have, but I have seen a couple shot with a 270 that took extra shots to knock over, but they were in the back of a truck dead right next to one shot with some magnum.............DJ

Remember this is all supposed to be for fun.......................