This has always been a popular question. Im definitely in the use enough gun camp. Yes you can kill them with a .22 with perfect shot placement but we and not perfect and I have seen a lot of hunters make poor shots because of the excitement even if they are excellent shots at the range. Not to mention the wind out west is not like the wind back home. To answer the question, I have to ask how far do you want to shoot ans are you ok passing on shots? If you want to be able to shoot out to 600 in the wind, the 6.5 creedmoor is not a great choice. Elk are much tougher than deer. I have seen them soak up lead like no other animal. They cover ground so fast its amazing, you do not want to wound one. Its not just about size, its the guts. While a moose is also a massive animal their heart is physically smaller. I remember helping my buddy gut his moose and while it was bigger than any elk I have seen, I was amazed how small the internals were in comparison to an elk. I think that why they can just take more than moose or deer. Im not saying you need the biggest magnums out there but I do have a preference for the .30s and .338s. After experiencing enough elk hunts and shooting a lot in Montana I pulled my personal max shot back to 6-700 and maybe if things were perfect Id push it to 800. Those shots I felt I could make without unexplained misses. Past that I had range trips that I would miss wind calls or have dope off enough to miss high or low. Inside 600 that did not happen. Could I kill them at 1200? Yes I could, but I could also wound one. So after making that decision, I have settled on the 300wsm with 185s as my absolute favorite elk rifle. I have had everything from 280ai to 338 lapua imp. I also love the 338 lapua imp, but I dont need it for 600yd shots. For the guys that want to go past that the 338 is my favorite but it needs to be 13 pounds at least. The big 300s fit in between. The 300wm to 300nmi. The reason the big 30s are popular is because they get you closer to the 338 but you can build them lighter. If a guys want the most in a 10lb rifle, build a 300 NMI. For me cartridge selection revolves around max distance and weight. If you want the gun to shoot it needs enough mass, the bigger the bullet the heavier the rifle has to be. The long the distance the better the ballistics have to be, its all a compromise.