Originally Posted by Nathan
In a nutshell, it is the 16" min barrel length without a tax stamp.
If that were not there, I would have a 40 or 45 6" -8" carbine which used Glock or other 30 rd mags. Aimpoint micro and a bright light.
Something Uzi or MP5ish comes to mind, but Uncle Sam has made those too hard to own. A small pcc with a 16" barrel is pointless. A tax stamp is a waste of time and money.
Exactly why pistol caliber carbines are not popular in the U.S. You have to either go through all the crap of owning a SBR, or own a full size 16" rifle. If you're going to own a rifle, it might as well be a rifle caliber due to the extra range. Sure 9mm ammo is cheap but once you start getting into .40 and then 45acp the cost of .223 ammo is about the same to buy in bulk, like $330 for 1k rounds. .223 kick isn't that bad either and you get a heck of alot more range.
So really the only reason to own a pistol caliber is if you care about not putting as many holes through your wall like if you live in an apartment building, or for mag and caliber commonality, which i think is dumb. Just buy half as much of each ammo. AR mags are dirt cheap at 10 mags for $90. Whereas 30 round pistol mags are super pricey.