Walking Fire attacks
Walking Fire is a term used when a 'Mech, or other Combat Vehicle is using an Autocannon with a high rate of fire (typically an Ultra or Rotary Autocannon, (standard autocannons using the rapid fire rule count as an Ultra AC)) to damage multiple targets in a single volley of fire. An LB-X Autocannon can also use this function for cluster ammunition to spread damage amongst adjacent targets.
Ultra AC (and Rapid Fire AC) Rules
Both targets must be adjacent to each other in order to use walking fire. In this case, both targets use the highest to-hit value when rolling for hits against each target. So, if one 'Mech jumped over 8 hexes into heavy forest, and the adjacent target is immobilized, prone, and adjacent to the attacker, both are treated with the hit modifier for the jumping 'Mech, its terrain cover, and the distance traveled, even though the immobile 'Mech would be a nearly free hit. Add a +1 to both rolls to reflect the inherent inaccuracy of walking the gun. Do not use a secondary target modifier for either target (unless this is in fact a secondary target according to the declaring player, in which case, it's added to both rolls). Roll a die for both targets after using these modifiers. If the target number is matched or exceeded for one target, it is hit. If the target number is missed, the target is not hit. These rolls are done for each target.
LB-X Autocannon Rules
An LB-X autocannon rolls similar to the above. Both targets are hit using the hardest to hit target as the baseline for the to-hit roll, with +1 for "walking" the shot. If only one target is hit, resolve it as normal for a cluster shot hit. If both targets are hit however, whatever damage that misses the first target is rolled against the secondary target. So, an LB-X 10 hits one target for 7 damage on the cluster table, leaving 3 to be rolled against the second target. If one target takes the full brunt of the shot, (in this case, the full 10 points) there is no more damage to carry over to the second target.
Rotary AC Rules
A Rotary Autocannon follows the to-hit roll for the rest of these autocannons, up to whatever burst size the player opts for. The hit result is determined with a single die roll checked against the cluster hit table. Shots that hit are to be divided evenly across all targets where possible. "Odd numbered" shots that hit are rolled randomly. If only one target is hit, pick randomly which was hit. A missed roll implies that the entire volley missed.