flechette

1.The Steyr ACR used new flechette ammunition that was nominally called 5.56 mm, with a very high 4750 ft/s (1450 m/s) muzzle velocity.

而施泰尔ACR使用了新镖弹，通常被称为5.56毫米弹药，但是具有极高4750码/每秒（1450米/每秒）枪口速度。

2.The ACR "rifles" used smoothbore barrels to fire single or multiple flechette per round, rather than bullets, to provide long range, flat trajectory, and armor piercing abilities.

炮弹（抛射物）须拥有稳定外形，比如带尾翼箭状物或球体，以此减小发射时震动。