I've seen guns that look like a 5.56 pistol, but are 9mm. Do these guns have any advantage? Would the longer barrel add any significant benefit?
I’m used to carrying around a longer barrel; but yes, at times it is hard to conceal.Longer barrel will give some more velocity. The longer site distance makes it easier for aiming. Longer barrels are generally more accurate at further distances. Only disadvantage i can think of is concealment when carrying.