One of my girls got Mcd, and shot a harbinger girl with 80HP in the front, one shot killing her
Even a sniper gauss has like 85 damage or something, but 37MM has like 120 or something. Also I'm using F3 but I think the gauss and plasma research is still broken, the only thing I still need to reach Cydonia is the star god codes and then onto the ship I need to build, and the only plasma gun I've unlocked is a light plasma gun. I've interrogated the mercs and star gods, got all the other cydonia codes and done pretty much all the other available research, even unlocked gauss and plasma defenses but it still didnt become available sadly.
I think the 37MM should be fine, it has like 100% snap shot damage and can be snapshotted right after equipping it from my inventory. It also makes short work of everything I've fought so far. I think heavy plasma autofire probably does more damage at close range but I cant have that and I think 37MM rifle is probably good enough. Guess I just need to keep looking for smuggler ships til I get lucky now and can finish the game