Hands up who thought I'd put an extra f in the title? Anyone? No? Oh, I was sure I'd catch someone out. Riffling, as you know, means to turn pages in quick succession (my book Paint Me a Picture is such a page turner you're sure to riffle through it) to shuffle cards or something to do with gold washing. A riffle can also be a patch of waves or ripples (I particularly like that one)
Rifling on the other hand is putting spiral grooves in a gun barrel to make it more accurate (the gun in question could be a rifle, but they do it with other kinds too). Rifle can also mean to search and rob or carry off as booty. So someone might riffle through a gun inventory deciding which rifled rifle to rifle.