Best rifle caliber for western hunting?

[Rodeotime]

Best is subjective, that being said your .270 is just fine out to a much greater distance than 300 yards if you’re proficient.

 

[thinhorn_AK]

I shot a dozen elk with a 270 and cheap Winchester silver tips. I never felt like I needed more.

 

[buffybr]

Not looking for an argument. I’m all good here. You do you partner! Jack O’Connor never shot anything but a .270

A bold statement, but like a couple of other replied, that's simply not true.

A quick look In O'Connor's book "The Art of Hunting Big Game In North America" he listed at least 13 other cartridges other than his beloved .270 Win that he killed North American big game with:
.30-30
7x57
.30-06 He said that he killed more deer with that than he did with a .270
.300 Weatherby
7mm Rem Mag
.257 Roberts
.348 Win
.22 LR
.35 Whelen
.250/300
.35 Rem
.256 Newton
.32-40

Then there were his African and other International hunts...