I'm not sure if this is a bug but it seems like it might be.
Currently all beam cannons available IG fire a cure moderate healing beam instead of any kind of damaging beam. I seem to recall they used to do something that had a more universal damaging effect (I think it was searing ray spell). I was going to use them for flashy "Second Machine Age" style Beam Cannon executions in capital cases....but that is currently impossible without a damaging version available for crafting.
So at the moment I have two very expensive healing beam cannons that are....less than useful at carrying out a beam cannon firing squad execution =(
I know what this is about and will speak to SC about it if I remember...