.40 S&W is an interesting cartridge. It started as a shortened version of the reduced-power load of the 10mm Auto round, and it’s often been branded as “short and weak”. On the other hand, it’s been a bridge in the caliber debates between .45 “size/weight guys” and 9mm “capacity/velocity guys”. It’s now fallen out of vogue somewhat. Let’s take a look.

The .40 S&W has been a super popular law enforcement caliber for the past twenty years or so. The FBI led the adoption. In the .40, for a round a trifle bigger than 9 mm, cops got a more powerful round that was a lot more effective. But the overall length was similar to that of 9 mm, so you didn’t need a big frame like 10 mm auto did. This meant that smaller hands had a chance of controlling guns firing the .40 round with good technique. And it could happily pass all of the FBI’s ballistics tests where 9 mm generally couldn’t.

But technology advances. By now, 9 mm hollow point rounds have caught up with .40, and can also meet the FBI’s ballistics test standards. This makes the advantages of the 9 mm round readily apparent:

1. More rounds¹
2. Lower cost
3. Lower recoil

That said, the .40 still holds some advantages over the 9 mm round. Clearly, if you are a LEO, your agency might issue something in .40. In which case, it behooves you to carry and practice with .40. And if you just like the round, by all means. Carry it. I’m not going to stop you.

1. Makes Major power factor easily
2. Does very well against intermediate barriers.

Let’s pull these apart. For USPSA and similar competitions, shots landing outside the A-zone of the target are penalized less if your power factor is high enough to “make major.” Power factor equals bullet weight in grains times velocity in feet per second divided by 1,000. Presently, it must be over 165 to make major. It is possible to do this with a 9 mm round carefully loaded, but this is somewhat dangerous, as you’re exceeding the pressure specs for the cartridge, with all the hazards that entails. Most commercial .40 loads will easily make Major, and it’s also a lot easier to handload .40 rounds that make major. As a result, .40 S&W is a popular caliber for competitors.

Intermediate barriers are pesky things you need to get to in order to reach your target, like auto bodies. For a CCW holder, this probably won’t be an issue that often. But it might be for law enforcement agencies, and it’s a reasonable consideration for issue weapons.

So, while 9 mm might make more sense, .40 is still an effective choice. If you like it, rock on. If you don’t, there are other choices that work well too. And it’s a great way to make major.

For the curious, I own an M&P 40, and might make another for open division gun games. I usually carry and train with 9 mm.