Still, there must be some way of comparing how well different cartridges will perform on game, right? Sure there is, but only to a point. TKO works better than energy, in my opinion, as a point of comparison, and comparison is all we're going to get. A definition of a bullet/cartridge's killing power just doesn't exist.
Getting back to the title of this article, "What Size Gun do I Need to Kill a Deer," the answer is largely "bullet placement." There are many, many cartridges that will kill deer and kill them cleanly, but neither the biggest bore nor the fastest magnum will do so cleanly if you don't hit the critter in the right place.
Hitting 'em Where They Ain't
Now, I have been guilty of hitting deer where I shouldn't have... where I didn't mean to, but I did. I have made mistakes. If you hunt long enough, you will, too. At times like this, when your bullet placement isn't wonderful, you do not want to be using a marginal cartridge - period. That's one reason I like to have more gun than I may need when I hunt deer... because then the extra "oomph" can make a big difference in whether I get my deer or not. This has served me well over the years, as I have never lost a deer yet.
None Too Big...
Mom and Dad taught me something that I believe in, and which applies here: It's better to have it and not need it than to need it and not have it. There are also some words of the well-respected gun writer Ken Waters which ring true, the gist of which is this: There's no such thing as overkill - you can't kill game deader than dead.
But Some are Too Small
Devotees of diminutive cartridges such as the tiny 22s, 243s, 6mms, and various 25s would do well to consider this, for if they choose to follow that sage advice then they really ought to be looking around for rifles chambered for more powerful cartridges. Do not start kids hunting deer with small cartridges - it is a mistake. Young 'uns and women can handle shooting honest-to-goodness deer cartridges. 'Nuff said on that.
How Dead is Dead?
Back to bullet placement... hit a deer in the vitals, break its neck or back, and you have a dead deer. How dead can a deer get? Fortunately, that's one point that brooks no debate - dead is dead. But what is required of a cartridge to make it a reliable, efficient game-getter even when hits are not in just the right spot? Let's look at some numbers and see if we can come up with anything concrete.
44 Remington Magnum
I'll start with my pet 44 magnum Ruger carbine, which has killed a lot of deer over the years. Dad taught me to use the heaviest practical bullet in that carbine, which is 240 grains. Referring to my copy of Bob Forker's very useful reference book "Ammo & Ballistics," I see that at 100 yards it produces a TKO of around 20.0 to 20.3, with energy varying from 988 to 1015 ft-lbs. Velocity at 100 yards is a mere 1370 fps or so.
Let's move on to another of my successfully-used deer rifles, a Savage 110 chambered for what many consider to be a spectacular deer-killer, the 270 Winchester. With the popular 130-grain bullet - which is too light for my tastes - average TKO at 100 yards is about 14.5. Energy is around 2200 ft-lbs, velocity roughly 2800 fps. With 150-grain bullets, again at 100 yards, the 270 carries between 2100 and 2600 ft-lbs of energy, with velocity ranging from 2500 to 2800 fps, and a TKO of 15.1 to 16.7.
To compare, the 44 mag looks like a wimp when it comes to energy and velocity, with its 1,000 ft-lbs of energy vs. a low of 2100 from the 270, and a mere 1370 fps compared to a low of 2500 fps from the 270. But when looking at TKO, the 44 beats the 270 hands-down, with its average of 20.0 vs a high of 16.7 from the 270. Which one will kill deer reliably? Either one, of course. Which one provides a greater margin of error, given a less-than-perfect shot? Within 100 yards, I believe the 44 mag does, with its heavier bullet and larger diameter, and resulting higher TKO. (continued)