So, I'm not sure if this was our house-rule, but, swarm-LRMs worked like LB-X cannons, with each missile rolling for a location. Now, if you fire two LRM-20's, both hit with at least thirty-six missiles, statistically, you'll get one head-shot. Now, if you can do that each turn, it'd be like a boxing-match until the pilot is, eventually knocked unconscious.