I've never shot an Elk, but that 150 grainer at 06 velocities won't cut it at 600yd, best utilised at 400 and under with impact velocities over 2400 for dramatic wounding on game in the 200-300lb mark.
180gr partion would be my pick driven as fast as you can, great within 400 and adequate to 700 for game of that size.
If you do opt for the lighter pills aim for the neck or brush up on your tracking skills.
Good luck
You're the official winner of the biggest bullschit post of the day award. That's quite the honor with Jayco and Swampy also active. Congratulations?
