That issue is the moderate bullet speed increase most of them impart to the bullet because of the 16″ barrel, as opposed to the 3″-5″ barrel in a pistol.

This speed increase is huge in 9mm, with some hot loads exiting the barrel at almost 1800 fps.

If you study the charts that all the bullet manufacturers put out, and the penetration data that is also available online, you will note that over-penetration becomes an issue with some bullets at just over 200 fps increase. A secondary problem is that over-clocked bullets don’t expand reliably.

Generally, you should shoot the heaviest bullet you can get in a defense round for any caliber you have a pistol-caliber carbine for. The heavier bullets don’t have as much of a speed increase as the lighter ones, and are less likely to over-penetrate or fail to expand.

You could solve this problem with handloading, but most folks prefer to use factory ammo for defense, for often-discussed reasons.

The NRA teaches that over-penetration is a huge issue for defensive shooting inside the home, but, like anything with roots in physics, it is a solvable problem, once you know it exists.

If there’s a burglar, you just jack the slide on your shotgun and you most likely won’t have to shoot him and clean up body parts, just the puddle of urine and maybe some of blood and/or the crap that leaked out of the burglar’s undies.

Something that doesn’t make that distinctive sound is not going to scare goblins so you’ll have to shoot.

I don’t want to kill someone even if he’s in my house, I’d rather scare the crap out of him and get him arrested. The sound of a shotgun slide being worked has to be one of the scariest sounds you could hear in the dark of the house you broke into.

So naturally I have a .44 magnum by my bed.