So-called average bull elk is rarely heavier than 700 lbs. Many cows and young bulls weigh in about 550 - 600 lbs. These are not moose sized at all.
The myths & legends about armor-plating are always make me laugh out loud!
Just about any good rifle cartridge will get the job done. Shot placement to destroy both lungs is a good choice for longer shots. But the old timers I knew in the 1960's shot into the neck-to-shoulder joint with their 30-30's or 300 Savage lever rifles and folded elk right where they stood. No kidding!
Things have changed across the Western USA states. More 4-wheelers plus early archery seasons have caused elk to be warier and less easy to approach. Sensible elk cartridges like the .308 or 30-06 are tough to beat at distances out to about 225 yards or so. The new 308 Marlin cartridge and older 444 should not be ignored.
A hunter who is conviced that a magnum is best for elk should focus upon more shooting practise than the non-magnum hunter. Sadly, the opposite is often the norm.
Good hunting to you.
Fire up the grill! Deer hunting IS NOT catch and release.