Much better to plan for the worst possible situation, especially with heavier game because I am pretty sure most moose do not fall to a single shot.
This is true in my experience. I have never seen a moose
drop at the first shot unless the bullet disabled their central nervous system - meaning the bullet hit the brain or the spinal cord in the neck or the back. And I've seen quite a few shot. Now I have dispatched moose with a single bullet broadside thru the lungs a number of times. If I know I've connected solidly with a broadside double lung shot, I'll generally hold my fire unless the bull is going to be able to disappear from view. Bulls so hit have typically bolted at the shot and run/trotted less than 75 yds, stopped, lowered their heads over a period of about 30-45 seconds, and then collapsed, tipped over, or bedded down and died. Shot one with a 12 gauge Brenneke slug once from about 120 yards. The slug entered a littler lower on the ribs than desired, but this bull reacted the same way, except the slug wasn't as destructive as a higher velocity centerfire rifle round, and we had to dispatch this bull with another round after walking up on him. Same with a bull I shot at 765 yds with a 250gr round nose Nosler Partition. The bull was still alive after trotting 60 yds and bedding down when I got out to him, but unable to get up and move out. This was about 20 minutes after the bull dropped to the ground out of site. The slower velocity hit at that range didn't destroy enough lung to cause rapid death.
Bull moose have a lot of blood in them compared to a deer. You can hit a deer in the rear ham with a sharp broadhead and the deer will bleed out and die from blood loss before the wound clots - stopping further blood loss. Hit a bull moose in the rear ham with a sharp broadhead and the bull will not lose enough blood to die before the wound clots. The bull will be sick, but will not die of blood loss, unless you happen to hit the femoral or another large artery/vein in the rear leg.
Moose aren't near as high strung as deer, in my experience. I suspect they have a slower heart rate/metabolism than deer. Stories of moose absorbing multiple lethal bullet hits broadside to the ribs/chest and never even running are fairly common, although I've never personally seen or experienced this. I heard one reliable story from two hunters I worked with that were hunting together. They shot a bull 5 times in the ribs at about 140yds (30-06 and 338 Win Mag). They were in credulous that they could be missing the bull, so they kept on taking turns shooting. The bull finally fell over without ever taking a step, and they found their 5 bullet hits upon field dressing. Every bull I've shot or seen shot by others lethally into the ribs bolted at the shot and trotted around 50yds (less than 100yds) before stopping, losing strength, and then collapsing.
Based on my experiences and observations, if a lung shot bull isn't slowing down after moving 50-60yds, you outta plan on shooting him again, even if he's out in wide open terrain. I've never seen a solidly double-lunged bull moose go more than 100yds from the initial shot location.
Watched my brother shoot a 60" rut-crazed bull with a sharp broadhead thru both lungs from 30yds. The bull bolted 15yds, stopped, and dropped like a bag of potatoes after about 15 seconds. Faster than I'd ever seen one flop with a high-powered rifle bullet thru both lungs. The part I couldn't believe was the bull never even twitched after he flopped down to the ground. Watched it all from about 50yds away. Go figure...