blunt instrument
noun
1- a heavy object without a sharp edge or point, used as a weapon（作武器用的）钝器。
1.1
- figurative an imprecise or heavy-handed way of doing something〈喻〉不精准的做事方式, 盲目的做法; 笨手笨脚：
as a promotional method direct mail is a blunt instrument.
作为一种促销方法, 直接邮寄有很大的盲目性。