overunder
(叠筒枪)双筒上下重叠的
例句
Now, I can have a M203 (an overunder M16 grenade launcher) which is not crew-served.
现在,我可以拥有 M203(M16 双筒上下重叠的榴弹发射器)了,不需要乘员就可以使用。