There is no right answer to that question!
I love them both! You see, with the Springfield Armory XD-S you can choose your favorite caliber, 9mm or .45 ACP, and get the same compact size and great features. They’re essentially the same gun. If you believe in the “.45 ACP is king” theory, great! If you prefer more 9mm rounds in the same size gun, great! The Springfield Armory XD-S can please both.
When I say same gun, I pretty much mean same gun. There are internal parts differences of course, but the exterior dimensions are identical in the .45 ACP and 9mm versions. Just last month, Springfield Armory announced the 9mm XD-S 4.0 model, which is still the same gun, except that it features a longer barrel – 4.0 inches instead of 3.3 inches.
Even key interior dimensions are the same between the two models. The magazine wells, and even the exterior of the magazines are the same width. The length (front to back) of the .45 ACP magazine is a bit longer due to the longer cartridge size, so you may need to account for that depending on what type of magazine carrier you use. Some are adjustable, others not so much.
I measure the thickness of the magazines at just about .558 inches. How’s that you say? The .45 ACP is much thicker than the 9mm! If you take a close look at the magazines, you’ll see that they are shaped to create interior differences. The 9mm magazines have ridges pressed into the sides that account for the narrower diameter of the 9mm cartridge. Clever eh?
The only observable difference between the two, excepting the caliber marking, is the thickness of the barrel. We’ll get to that in a minute.
For now, just know that any holsters and accessories you have for one work equally well on the other. The only possible exception is the new 9mm XD-S 4.0 model, which has a longer slide and barrel than the original.
Now that I’ve gone on and on about how similar these guns are, let’s point out the differences.
The primary difference is capacity, and that’s simply a result of the 9mm cartridge being skinnier than that big fat .45 ACP. You can fit more skinny clowns into a Volkswagen Beetle than fat ones. It’s the same with cartridges and magazines.
The standard magazine of the 9mm model holds seven rounds while the .45 ACP model holds five. Including a cartridge in the chamber, that’s eight and six respectively. Both pistols have an optional extended magazine that adds additional grip length. The longer magazine brings 9mm capacity to nine plus one in the chamber and .45 ACP model capacity to seven plus one.
You might wonder why the 9mm version is 1 ½ ounces heavier than the .45 ACP model. That seems a little backwards doesn’t it? From my observations, the exterior barrel diameter is the same for both calibers, but of course the interior diameter of the 9mm model is smaller. Therefore, the barrel of the 9mm model is “thicker” and a bit heavier.
The bottom-line takeaway is that most accesories are common between the two guns. With the (sometimes) exception of magazine carriers, pick the caliber you want. Holsters, lasers and other accessories will work on either model.