I want to like pistol caliber rifles, I really do.
There is not gun more fun to shoot than an HK MP5 9mm. The Swedish K and the Thompson submachine gun are just a freaking hoot to shoot. The UMP and the 9mm AR-15 are a blast. The CX4 and the Uzi call to me on some odd visceral level. For range day fun only a .22 can compare to the 9mm carbine when it comes to a ratio of dollars to grins.
The 16” semi-auto pistol caliber carbine just does not make sense for any fighting application.
Sure it will do the job of a long gun. The pistol caliber rifle will shoot easier and be much more forgiving than a handgun, but you will be sacrificing the maneuverability of the pistol when indoors or in a car while at the same time sacrificing the terminal ballistics of any rifle round.
Pistol caliber rifles will always fall short when compared to the AR-15, AK-47 or similar popular rifle. Even if we start talking lever guns the modern 30/30 far outclasses the .357 or .44 Mag. The terminal ballistics of rifles and shotguns are just superior than pistols. If you factor in making a medium to long rage shot, the bullet drop and terminal performance after a distance are ridiculously better with the rifle.
“Compared to pistol caliber weapons, virtually any shoulder fired carbine caliber weapon or 12 ga shotgun will prove superior from a wound ballistic standpoint.” DocGKR
It turns out, if you select solid .223 Remington or 5.56 NATO caliber ammunition it will exhibit less “overpenetration” than 9mm, .40 S&W, .45 ACP and 12 Gauge. Science! This is very true when we start talking obstructed shots. Like you might encounter in your house. Or your car. Get the picture?
I really, really, really like the .45 Auto SBR with a silencer. It is one of my favorite guns to shoot. Unfortunately unless you are fulfilling a very specific mission, the .300 BLK would be a more versatile and sound choice for a fighting rifle. The ability to shoot supersonic ammo and the benefits ballistically of the pointy .30 cal bullet far outweigh the cool factor of the .45 ACP.
The best gun for fighting in your home is the one you have at hand.
If you have choices at hand the best gun for fighting will be the gun you fight the best with.
If you get a chance to pick what you have handy and what you are good at using, pick a good rifle in 5.56x45mm. The AR-15 is easy to recommend as it is the best one you can get right now. [see:AR-15 Buyers Guide]
We always say at The Gun Show Podcast, if you are buying this for strictly range use or for fun, buy whatever you want! Just please be aware there are better options than the pistol caliber rifle for a fighting long gun.