Light.
Short.
Short range.
"Best".
Assuming that "best" includes some combination of the usual factors (caliber, bullet weight, terminal performance, energy, bullet selection, etc.) with a little bit of emphasis on 'power' and caliber...
I'd toss up a list something like this:
.300 WSM **
.325 WSM **
8x57mm Mauser
.358 Winchester **
.35 Whelen / .358 Hawk
.338 Marlin Express
.35 Remington
.375 SOCOM **
.375 Winchester
.375 Whelen (see .400 Whelen) / .375 Hawk
.38-55 WCF
.400 Whelen (original sharp shoulder - not the RCBS bastardization) / .411 Hawk
.444 Marlin
.458 SOCOM **
.450 Bushmaster **
.460 S&W
.45-70
.450 Alaskan
.458 Win Mag
.475 Tremor **
.500 S&W
.50 Alaskan
Cartridges marked with double asterisks (**) can be bought or built as AR-style rifles. With a little careful planning and/or a boat load of cash, ultra light versions (under 6 lbs) can be built or bought. .375 SOCOM and .475 Tremor are wildcats based on the .458 SOCOM case; designed and sold by Tromix. The .375 SOCOM is very new to the market, but was in development for over 6 years and already has a loyal following. .475 Tremor is more obscure, with only 4-5 rifles known completed (and 13 barrels, total), but those of us that have one LOVE IT! (Yes, that includes me.)
If you aren't trying to reach for the uber-powerful, then .308 Win, 7.62x54R, .300 Savage, and dozens of other cartridges are more than adequate.
My personal 'collection' of rifles, and one revolver, used for, dedicated to, or
built specifically for Elk include the following cartridges (multiple rifles in different configurations for some cartridges, with 'lightweight' examples listed by weight):
7.62x54R (short range)
.270 Win (all-around)
.30-06 (all-around - 7 lb)
.35 Whelen (intermediate range - 7+ lb)
.44 Mag (very short range)
.444 Marlin (short / intermediate range - 6 lb 3 oz)
.458 SOCOM (short range)
.475 Tremor (short range - 7 lb 8 oz, - with a thinner profile barrel and light weight lower, this rifle could be sub-6 lb.)
(I prefer putting big holes in things - even if it's at lower velocity.
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