He tells me that the ballistics on a .45 can't be beat.
Lets not confuse ballistic efficiency with total energy.
No doubt in my mind that the .45 will keep burger in your buns from the deer woods. An animal can be only made so dead.
But as far as not being able to beat a .45? A .440 round balls weighs 128 grains, a .490 weighs 179, and a .530 weighs 230 grains. Now, it may take three times as much powder to drive the .530 ball at the same speed as the .440, but at any range it will then have more energy, punch a larger hole, be better in any measurement of the ability to kill.
If your change machine is 90% efficient and you put a dollar in, you still have fewer coins than the guy that puts a $5 in a machine that's only 75% efficient.
Another way to look at it is that if the pan delays and the deer takes a step before the ball catches it just behins the diaphram, you just can not HAVE too much extra available energy at your disposal to hopefully make that blood trail shorter. Larger bores that the .45 give you a little edge when bad things happen. Bigger holes, more blood vessel disruption, more energy transfer.
It's like when you make coffee and you "add a scoop for the pot". Or when you tune an engine for maximum RPM and then drop back "three clicks for Grandma" because running too lean will harm the pistons and cylinders. It's good to have a margin for error.