1
general::
Take careful aim, as in The debater drew a bead on his opponent. This term, dating from about 1830, alludes to the bead on a revolver or rifle, that is, a small knob in the foresight. [c. 1930]
American Heritage Idioms
2
general::
Phrase(s): draw a bead on someone or something [and] get a bead on someone or something
1. Lit. to locate someone or something in the sights of a gun. • Fred drew a bead on the target and pulled the trigger. • The hunter drew a bead on the deer. 2. Fig. to prepare to deal with or obtain someone or something. • As soon as I get a bead on how widespread the problem really is, I will set up a meeting about it.
McGrawhill's American Idioms And Phrasal Verbs