10mm for Bear Defense
The most powerful common semi-auto pistol caliber — what 10mm can and can't do against bears.
The Short Answer
10mm Auto is the most powerful widely available semi-auto pistol cartridge, and it's a popular choice for backcountry and bear defense because it pairs serious power with the capacity and fast reloads of a semi-auto. Loaded with heavy, hard-cast or bonded bullets designed for deep penetration, a 10mm like the Glock 20 gives a hiker or hunter a capable, packable sidearm against aggressive wildlife.
Honesty matters here: against a large, determined grizzly, many experts still favor a heavy-caliber revolver (.44 Magnum and up) or, better yet, bear spray, which has an excellent real-world track record. For black bears and as a versatile woods gun, 10mm is well-suited; for the largest bears it's a reasonable compromise that trades some terminal power for capacity and shootability. Use ammo built for penetration, not expansion.