A pistol caliber SMG makes perfect sense as a possible trunk gun (next to the carbine rifle or shotgun respectively) in a CQB urban type environment for close range, suppressive fire & the likes. I have noticed that these semi-auto civvy carbines have started to grow in popularity a few years since the ugly neutered HK came out, and I was wondering why. Other than cool factor/fun range toy, is there any useful purpose for one of these things as a semi-auto weapon? Don't get me wrong... "because you can, because they're cool, because I'd like one" are reason enough for them to be justifiable purchases. I am just trying to see if there is any REAL practical use in which they actually hold an advantage. I just don't see them doing anything a 16" AR can't do. Does anybody have some light to shed?

I wouldn't trust a PCC for anything larger than clearning a room. A 16" AR can do a whole heck of a lot more than a PCC and reach a lot more people if needed further out.

You can shoot them at Pistol Caliber only ranges.

Just really big pistols. I had an sp89 and my glock 17 is better. If you are going to carry a bulky ass heavy pistol , do yourself a favor and just get an sbr.ymmv.

Quoted: I wouldn't trust a PCC for anything larger than clearning a room. A 16" AR can do a whole heck of a lot more than a PCC and reach a lot more people if needed further out, without being a whole lot larger.

Quoted: A pistol caliber SMG makes perfect sense as a possible trunk gun (next to the carbine rifle or shotgun respectively) in a CQB urban type environment for close range, suppressive fire & the likes. I have noticed that these semi-auto civvy carbines have started to grow in popularity a few years since the ugly neutered HK came out, and I was wondering why. Other than cool factor/fun range toy, is there any useful purpose for one of these things as a semi-auto weapon? Don't get me wrong... "because you can, because they're cool, because I'd like one" are reason enough for them to be justifiable purchases. I am just trying to see if there is any REAL practical use in which they actually hold an advantage. I just don't see them doing anything a 16" AR can't do. Does anybody have some light to shed?

Pistol rounds are often helped tremendously in effectiveness by being fired from longer barrels. A carbine allows you to maximize the ballistic potential of many pistol cartridges. Some of the semi-auto carbines can even take hicap pistol magazines that a person may already have on hand. (A big plus during the AWB or in those states where there is an AW ban...)

As far as using it on the street, a carbine is usually more accurate than a pistol, giving the round some extra range.

A carbine is better than nothing tactically speaking, but I believe one is better served by a short rifle for serious social applications.

Quoted: Just really big pistols. I had an sp89 and my glock 17 is better. If you are going to carry a bulky ass heavy pistol , do yourself a favor and just get an sbr.ymmv.

An sp89 is not a PCC. it is just a big pistol.

is there any useful purpose for one of these things as a semi-auto weapon? ... I just don't see them doing anything a 16" AR can't do.

Pistol caliber carbines goes back a long way.  The Winchester rifle was commonly available in pistol rounds such as .32 WCF (Winchester Center Fire), which shared the same case with the .32-20 pistol cartridge, .38-40, etc.  It was quite common to have the pistol in your holster and rifle in your saddle scabbard to share the same cal.  My grandfather did exactly that... we still have his 1873 Win lever action in the family.

One advantage was that the same ammo could be used in both.  When used in a rifle, more velocity and range was obtained.  

Also, defensively, there is that range, 20-100 yds, where a rifle is needed over a handgun, even if only a pistol caliber.  It is a range where more shots are likely to be fired, at a faster rate, as compared to longer ranges where a true rifle cal would be better.  A light recoiling pistol cal is an advantage over a pistol.

I don't think there is anything a pistol cal carbine can do that an AR-15 carbine can't.

As far as wall penetration, go see the "Box o' Truth" series.

A .45ACP carbine that takes 1911 mags, or a 9mm Para carbine that takes your pistols mags could be very handy!