Is it better at medium range than the assault carbine?
Depends what you're facing. If it's an armored target, yes (with JSP BAR can do roughly 60 damage per shot), but if the target isn't armored, it's worse. Assault carbine has much lower spread (1.5 compared to 2.5) higher RoF, and bigger clip, but is lacking in DPS. But with the BAR, the spread is too big to use effectively with the low RoF, because you simply can't put as many bullets onto the target due to larger spread.