Damage Up stacking caps for certain weapons at some point. This is believed to be due to the amount of shots being needed to splat someone with that weapon being made fix. So if a weapon takes three shots to splat someone without any abilities then it will also splat at three shots with 3main abilities. Chargers are not affected by this. (Likely because in the charged state they all kill at one shot.)
This effect can be seen with the Aerospray already when applying 2mains. The damage caps at 24.9 => 24.9 * 4 = 99.6, thus five shots are required. If 0.1 more damage where done that number would go down to four.
