I found the below command much more convenient. If you want to copy lines from 6 to 12 and paste from the current cursor position.
:6,12 co .
If you want to copy lines from 6 to 12 and paste from 100th line.
:6,12t100
Source: https://www.reddit.com/r/vim/comments/8i6vbd/efficient_ways_of_copying_few_lines/