"Is 10mm a Viable Self-Defense Caliber?"--Lucky Gunner Ammo (7 min.)
The title of this video is really for click-bait. There is no question that 10 mm can be a viable self-defense cartridge, and the producer of the video does not question it. Rather, the issue is whether it is better than other cartridges or brings something to the table that other cartridges do not. In this video, the producer compares it to the .40 S&W.
As you probably know, the .40 S&W is essentially a shortened 10 mm--well, not exactly, but good enough for background--and it uses the same diameter and, often, weights of bullets. So, Lucky Gunner put it through its gel testing (4 layers of cloth over ballistic gel) and measuring velocity. What they discovered is that several factory loads had the same velocity as .40 S&W, meaning that you got basically the same performance. Where the velocity was higher, because it is still using the same types of bullets, the results weren't deeper penetration, but more consistent expansion. So, in that respect, the 10 mm offers the advantage of higher velocity resulting in more consistent expansion than the .40 S&W, but not all manufacturers take advantage of this.
This video only discusses the 10 mm in respect to defense against a human. The producer recognizes that defense against an animal, or hunting, is a different issue and admits that he does not have the experience to comment on those uses.
Paul Harrell has done a couple of videos that are somewhat related. You may have seen his recent video on .45 ACP versus .40 S&W which seemed to indicate that the .40 S&W really didn't outperform the .45 ACP. He also did one comparing the .45 ACP against the 10 mm. Harrell noted, with the ammunition he was using, substantially higher velocity with the 10 mm--between 100 and 200 fps greater than the .45 ACP. However, shooting hollow point into his famous (or infamous) meat target, performance was pretty similar, with none of the rounds from either the .45 ACP or 10 mm penetrating the pork ribs at the back of the target. However, he also tested plain old vanilla 230 grain .45 ACP Winchester White Box which did pretty well mangling the second watermelon "lung tissue" and penetrated through both sides, suggesting that it would perform pretty good against large critters.
So, in conclusion, when using commercially loaded ammunition, you probably won't see a big performance gain over the .40 S&W or .45 ACP, and, for a hunting or wildlife defensive cartridge, the 10 mm probably won't do any better than the .45 ACP. I suspect that to really squeeze performance out of a 10 mm for hunting will require either handloading, or specialty hunting loads.