rifling

n [U] these grooves 来复线; 膛线.

rider, ridge, ridge-pole, ridge-tile, ridgeway, ridicule, ridiculous, ridiculously, ridiculousness, riding, riding-crop, riding-school, rife, riff, riff-raff, riffle, riffraff, rifle, rifle-range, rifleman, rift, rift valley, rig, rig-out, rigging, right, right angle, right away, Right Honourable, right of way, Right Reverend, right-handed, right-minded, right-mindedness, righteous, righteously, righteousness, rightful, rightfully, rightly,