Richard Mann at Shooting Illustrated has evaluated a few different pistol cartridge chambered carbines and compared then with the M4-style carbines in 5.56mm and pistols chambered in the same rounds.

Bushmaster Carbon-15 carbine

Richard says …

With the versatility of an M4-style carbine in 5.56 NATO a given, it still may not be as cool as some pistol-caliber carbines. For fighting bad guys at rock-throwing ranges, it may be no better. A gun’s cool factor will not save your life, but nevertheless, a cool, pistol-caliber carbine loaded with the right ammo should work just fine. They are indeed more accurate and easier to shoot than any handgun.

Read it here.