Not to sound disbelieving, but am I understanding correctly that the rifles shoot the same calibers as the semi-automatic handguns? Is there any meaningful difference between the velocity of a same-caliber bullet shot out of a different gun?
There are many pistol caliber carbines, just as there are more than a few rifle caliber pistols. The increased barrel length typically found on the carbines provides some increased velocity but not as much as you'd expect because the powder has ceased burning (having been designed to be consumed within a pistol barrel's length). You do get increased accuracy over a pistol, ease of shooting, and cheap cross training.