Lighter calibers will kill elk as does a 25-20, 308 is as light as I care to go for elk, 30-06 means a heavier long action bolt gun without much of a step up from the 308, if you going to carry a long action bolt gun, and you reload, the 300 Win Mag does add something and is not any harder to reload and is very accurate, even with pleasurable light boolits. The 308 is still used by military all over the world, plenty of load data, components, information, all kinds of rifles, bolt, lever, semi-auto, old and new. If a store has '06' ammo it will have 308. Not much 'cheap' or surplus '06' around, plenty of 'white box' 308. I know what the paper numbers say about kinetic energy of the lighter numbers over longer ranges. I also know that there are other ways used to measure hunting effectiveness, Taylor's Knock Out, Keith's pound-feet (momentum),a few others, where they don't hold up as well as the heavier bullets and larger calibers. There is a BIG difference between dropping a deer or antelope and killing a bull elk. While I think the 243 is just fine for deer and antelope, I think the 308 is the lightest I'd use on elk.