I'm reading through the rules for Gunnery and I think I understand how half EDR results work...
But, I am not at all sure how they occur?
I can see that bow rakes could generate half results and I can see some half results on the damage table
Is this all, or are single guns and half damaged gun boxes supposed to do half damage as well as having half the likelihood of getting an effect? The rules for single guns and half damaged gun boxes cunningly say that they are effective (on odd rolls, vice missing on even rolls), but don't actually say what the effect might be.
You're right, the only way a half EDR can occur is as a result of a bow rake. Originally the CRT had an Equivalent Damage Table (much like the ones used in GQ3.3 and FAI) that had several 1.5 and 2.5 multipliers. This habitually resulted in many half EDR results. A late revision did away with that table (and the annoying half EDRs). The only place we couldn't eliminate them was the Bow Rake multiplier. Try as we may, that one couldn't be done away with. (As an aside, when a half EDR comes up, my group rolls a die; even we round up, odd we round down. A bit of a cheat, but it does simplify things).
As for the effect of single guns (like chasers and half gun boxes); the damage results are the same as the rest of the gunnery, there is no modification to their effect (that's covered by the 'even/odd' hitting reduction).