10mm, The Best Millimeter?

10mm is the round that everyone seems to love to want, but few appear to own. It seems that every time a new gun is released, people whine about 9mm (the most common handgun caliber on the planet) and comment something along the lines of, "if they do it in 10mm I'll buy one". Yet 10mm handguns sit on the shelf and retailers that carry 10mm (if demand was high, more would) have dusty boxes because folks aren't buying it (pre 2020 panic hoarding).

So is 10mm really all that great? The round became famous after the 1986 shootout between two former Soldiers and eight FBI agents. In less than five minutes a total of 145 shots were exchanged, 5 FBI agents wounded, two killed, and the two suspects killed. The complaint was that service handguns weren't powerful enough. At the time that mostly referred to .38 Special revolvers, but it inspired law enforcement to convert to semi-autos, and more importantly inspired the adoption of the then-young 10mm cartridge.

Launching a 10mm, 180gr projectile at 1,300 ft/s yields 708 ft/lb of energy from a test barrel. That's about 50% more energy than most 9mm cartridges and nearly double most .45acp loads. The broader surface area (compared to 9mm) helps with not only core wound diameter, but also reduces the chances of a projectile with so much energy from penetrating too deeply. With a cartridge diameter less than .45acp higher capacity is afforded, though not as high as 9mm. More power and decent capacity, what's not to like?

Recoil is the answer. Reports of accelerated wear on both the shooter and the firearm resulted in somewhat of a download and 10mm became a little weaker. If you didn't know, making 10mm Shorter & Weaker is how .40 S&W was created (same diameter, 3.6mm shorter case length). Reduce the power some and you still have more recoil and less capacity than 9mm while retaining the more expensive ammunition. It's hard to tell which 10mm loads are "reduced" loads and which aren't. Even stalwarts of the cartridge that have supported it for decades like Double Tap have proven to be rather soft in their loadings. It's almost as if the folks who scream for 10mm don't even know what the round is supposed to be.

While working on an article for Combat Handguns Magazine (Jan/Feb 2021 issue) we chronographed 13 different 10mm loads. The intent was to see what CMMG's 10mm Banshee produced from an 8" barrel. Aside from Hi-Point's Carbine, there weren't many long-barrel 10mm options out at the time. The results, some of which are seen in the magazine, are below.

We expected to see results similar to 9mm which continues to gain energy significantly out to about 11". As you can see, aside from Hornady's XTP load, the energy gain may or may not warrant the increase in firearm size. Going from a 6" 1911 to an 8" AR-style platform is a HUGE increase in firearm size for what is a generally negligible increase in power. Is this the caliber's fault? Hornady Critical Duty 10mm from a 4.25" barrel isn't really much better than a good 9mm load from a 4" barrel. The 9mm pistol is lighter, easier to shoot, and the ammunition costs significantly less and is more widely available.

We theorize that unlike 9mm which has been used in submachineguns and longer barrels for decades, 10mm simply hasn't had the application. As a result the 80-year younger 10mm hasn't been loaded properly for longer barrels. Looking at our chart you see that after about 6 inches of barrel there's not much to be gained with 12 of the 13 loads tested. Despite 10mm being around since 1983, ammunition manufacturers simply haven't developed a load for longer barrels.

Is it worth trading in your 9mm? I think that comes down to your intended application and the firearm you will be using it in. 10mm certainly can offer more than 9mm, but you've got to have the right load in the right gun to get there. Otherwise it seems to us that you're just spending more money on ammo. The base energy level is higher, but not higher than two shots of less-expensive, softer-shooting 9mm that can likely be shot in rapid succession. Two wound cavities and bullet paths with more total energy. Did we just kill the 10mm argument? Let us know your thoughts and experiences. One thing that our test did not include was terminal performance of the projectile. 155-200gr permits a lot more with projectile design than 9mm's 65-165gr.