vi - vim using line back in register -

i register this:

a  b 

so typed : let @c='a^mb' , tried \r , \n instead of ^m

when type "cp vim not consider return line chars.

update:

i running vim 7.4.52 on 3.16.0-38-generic #52~14.04.1-ubuntu

:let @c="a\n\nb" 

seems working fine me on vim7.4 on freebsd. (double quotes instead of single quotes)

if it's not working, might want specify platform , version of vim?