XBOW

A crossbow is a weapon consisting of a bow mounted on a stock that shoots projectiles named bolts or quarrels.

Battlefield 3
The XBOW is set to be released as an All Kit weapon in the upcoming Battlefield 3: Aftermath DLC.

It is seen in the trailer equipped with a PKS-07 in the hands of the Recon, while the Engineer and Assault it equipped with either a Red Dot Sight or KOBRA.

It is stated that there will be four types of arrows: Medium Range, Long Range, Explosive and Proximity.

According to a post in the Battlefield Blog, it is described as a jury-rigged weapon made from a malfunctioning assault rifle, most likely an M417, wire from a broken down car, scrap metal for the bow, and a optical sight like the Red Dot Sight or PKS-07 as shown in the trailer and preview screenshots.

Trivia

 * The XBOW seems to be inspired by the TAC-15 upper receiver for AR-15 style rifles. However, in game the XBOW is fitted onto a non-working M417.
 * The lower part of the XBOW, the M417 receiver, has its ejection port, bolt release button, and magazine well taped shut.
 * The ammo counter's fire mode selector has multiple fire modes, hinting quickly interchangeable ammo types.