User:LRichardson/Essays/Gun, Automatic, Utility, Model 20 (GAU-20)
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Authors note: This item is fan created, non canonical piece of equipment. While derivative of and compatible with BattleTech as published it is not official and is obviously unsuitable for tournament use.
Gun, Automatic, Utility, Model 20 (GAU-20)
The GAU-20 is a medium caliber, heavy barreled rotary type cannon of the sort typically encountered in ground attack aircraft. Rather than firing a single shell at the target the GAU fires a tremendous volume of fire concentrated on a small area. In this way, the GAU behaves somewhat in between a multiple missile system and a traditional autocannon. Though a substantial portion of the damage inflicted will hit a single spot, some of the rounds fired will hit areas immediately adjacent to the primary impact zone. In addition to it's effectiveness against armor, the GAU is also brutally effective against infantry and low flying aircraft. The GAU uses the same ammunition that machine guns feed from and can feed from a common bin if a conventional Machine Gun is installed. The GAU also has the advantage that it creates relatively little residual heat. Since the barrels are exposed to ambient conditions their rapid spinning during fire significantly cools the weapon during and shortly after firing. As there is some spread to the impact zone the weapon is somewhat easier to hit with than a conventional single projectile system. As this system was devised as a retrofit to obsolete units, the mounting lugs, all up mass and dimensions of this weapon are bolt-in compatible with conventional Type 20 Autocannons.
The GAU-20 fires 20 rounds of Machine Gun ammunition per "shot". On a successful hit, roll on the cluster hit table to determine how many of those 20 rounds hit a single location and roll the location of that hit normally. The remainder of the rounds land on the adjacent hit locations to the left and right of the rolled hit location, split evenly between the two. If there is an odd number of remaining rounds from the cluster hit table, the remainder 1 round is allocated to the adjacent location of the choice of the player who won the initiative. If the main hit location is the head the remaining rounds miss the target. If the main hit location is an arm, half the remaining rounds miss the target, the other half hits the corresponding torso. If the main hit location is a leg, half the remaining rounds miss and the other half hit the other leg. Against infantry, only count the rounds that hit the main target location as hits and ignore the rest.
Against armored targets each round of ammunition only does one point of damage rather than the usual 2 for a Machine Gun. Against infantry however the damage is tripled. There is no base to hit modifier for this weapon, however if the roll to hit is one less than needed for a hit, roll on the cluster hits table and allocate damage in groups of 4 accordingly for both armored targets and infantry (with the infantry damage in this case being just like an LRM, 1 point per hit.) GAU has a -4 base to hit when trying to clear a hex. GAU's cannot cause fires.
- A KGC-000 King Crab with two GAU-20's (replacing the original AC/20's) engages a `Mech with a to-hit of 8. The attacker rolls a 9 and a 7. In this case both hit, but the one that rolled a 7 is a marginal hit. The first GAU was a clean hit and is resolved normally. The attacker rolls a right arm on the hit location table and a 5 on the cluster hit table, this means that 9 damage goes to the arm and 5 damage to adjacent locations. This means 5 hits to the right torso and 5 hits to the right of the right arm and are thus ignored. In addition a single point of damage needs to be allocated by the player who won the initiative, in this case a choice between the right torso or missing. The second GAU hits but rolls for damage similar to a cluster weapon. The attacker rolls a 10 on the cluster hit table meaning a total of 12 rounds hit. These are grouped in blocks of 4 damage. The attacker rolls a left torso, right torso, right arm and head. The attacking `Mech then marks off 40 machine gun ammunition used.
- Had this `Mech fired the two GAU-20's at a platoon of infantry, again with a to-hit of 8, and as before rolled a 9 and 7 respectively the attacker would roll on the cluster hit table for both GAU-20's. The first rolls a 5 on the cluster hits table and does 9 * 3 = 27 damage to the infantry platoon. The second GAU-20 rolls a 10 on the cluster hits table for 16 hits, but only does 16 damage to the infantry platoon because it is a marginal hit.