1) Type ."target <convergence range>"
2) look around, you'll see a giant white target following you
3)centre your guns site and loosen off a burst.
4)zoom in on the target and you'll see the dispersion pattern of your chosen convergence range, plus you'll be able to see if your site is bore sited correctly should you be using a custom site.
5) type ".target 0" to turn it off.