Why are my colonists being killed by rock throwers?

[nuschler22]

I have ten colonists and for some reason, I get attacked by about 8 or 9 raiders throwing rocks and get my butt kicked every time.  I'm stuck. 

All my colonists have guns and are behind embrasures.  Locked doors.  Turrets. 

And every time the raiders over run them.  Never had a problem with this in the past, it's like they are invincible wielding only rocks.

[Coenmcj]

Can we have pictures, more details?