I'd say this entirely depends on how skilled the siege weapon is. A 1 silver chevron cannon will do more damage with exploding shots then regular, sometimes causing a unit to rout after 1 volley (i was getting upwards of 50 casualties but in one unit), as apposed to a regular round which would kill approx 5 kills x 3 units (15 casualties).


This isn't to say that this is the fact, but its my personal experience with it, (i don't use cannons much in the field, i'd rather have an extra hvy cavalry)