Something custom. Something magnum, from 6.5 PRC all the way to 338 Lapau. Optic something in the 5-25ish range with a FFL reticle. That’s what I’d do. I personally have a 28 Nosler with a 6-24x on it.
For Montana elk at 500+ yards, I'd go with a .300 Win Mag or 6.5 PRC in a Tikka T3x or Kimber Montana, paired with a quality Leupold or Nightforce scope
Same as @Godzilla, I'd go with a .300 Win Mag. Paired with a quality Nightforce scope, you've got a combo that'll reach out there and get the job done.
