[Wize]

DamagePercentToUnits = x% does exist in Generals, however the DamagePercent is only viable in "Contain Methods" and even so ATM I have only seen them on Garrison and Transport Contain Methods.

Now to Answer The Question:

What you are attempting to do is great and I have no trouble with it.. except that the way that garrisoned and slaved systems are killed isn't like you think. That's why the above method on the RedGuardMachineGun didn't work.

Also, you'll have a problem with adding it to the small arms category (hence why the Ranger was given the Flashbangs). In order to kill the Garrisoned and Slaved Systems you first must have a projectile of some sort (albeit any "hidden" one will do). The hidden method is how the Toxin Tractor and Dragon Tank are able to clear out Garrisoned Buildings.

In order to kill Garrisoned Buildings the following lines must be present in either AIMissileUpdate (Dragon/Toxin):

    GarrisonHitKillRequiredKindOf  = INFANTRY
    GarrisonHitKillForbiddenKindOf = NONE
    GarrisonHitKillCount                = 2
    GarrisonHitKillFX                     = FX_DragonFlameGarrisonBuildingHit

Or DumbProjectileBehavior (FlashBangs):

    GarrisonHitKillRequiredKindOf    = INFANTRY
    GarrisonHitKillForbiddenKindOf  = NONE
    GarrisonHitKillCount                 = 10  
    GarrisonHitKillFX                      = FX_FlashBangGarrisonBuildingHit

Please note I say AFAIK to the above because I have never actually found the need to find extra clearers and henceforth I'm not sure of any extra "tags" you might need.

Here you find the problem as the Quad and other Small Arms units don't actually use projectiles. However I noticed one thing in ZH that AFAIK isn't in Gen (It's what allows the Microwave Tank to clear out buildings). There is a new Damage Type: KILL_GARRISONED. But that would create problems in terms of targeting and what to use to kill what.

Hope it helps, drop me a line if you need any help with anything

~Wize/Skywaters