338 Lapua mag, 375 H&H, 9.3x62 Mauser, 35 Whelan, 300Win Mag, 7mm Rem Mag are the calibers I own suitable moose and that’s the order I would chose them in. The author is right about the 6.5 Creed I own two in AR10s and neither gets the nod for moose. Elk in none bear country maybe.
If I’m taking an AR to anywhere bears are it will be my 338 federal in AR10 or 458 Socom if I really wanted to be light and carry the 12.5” Socom in AR15 but only with 400 grand hard cast hand loads that duplicate the 45_70 400gr@2300 fps it beats the tar out of the bolt group even with the gas block turned all the way down. So that upper usual shoots 250s@2200 perfect for feral hogs on walkabout haven’t recovered a single round all were pass through.
My 375H&H gets the nod anywhere there’s something with claws, teeth or hooves that’s big enough to eat or stomp me. Recoil is unnoticed when then go sideways.
I’d use 6.5 creed on anything, and game up here is bigger than most (northern Alberta). If I’m shooting an elk past 800 yards, I’ll use 300 Norma. 6.5 with 143 eld-x will do anything though.
I have an ar-10 in 338 fed; just too heavy; road huntinggun. I killed a couple moose over the years with the 338 fed; 210 nosler partition. Moose would do the 3 step shuffle and drop.
I knew some Indians that shot a sow polar bear with 556 ar; saw the picts.