X-ray death
I posted Scott's bit about radiation levels from X-ray lasers to the GURPS list and got the response (paraphrased) that while that radiation damage may kill you, it'll take time. Guns are supposed to make you die RIGHT NOW. So while the X-rayted guns may pump massive radiation out, it won't mater since you're already dead. The wounded, I imagine, can get some sort of treatment - don't things like cellular regeneraton come into play about the same time? J Roberson