Several types of modules can have ammunition or scripts loaded into them which effect their statistics. Most common are offensive modules such as guns and launchers. Different types of ammunition can grant different bonuses to the module that they are loaded into. Bonuses can also be both negative and positive. For instance some ammunition will grant a -50% optimal range bonus to any turret it is loaded into. This will effectively half the optimal range of the turret. If a player has a group of turrets then loading all of them with this ammunition it will not stack the bonus. So the optimal range of the turrets will not halve every time another turret in the same group is loaded with Antimatter.
Stacking penalty refers to the game mechanic in which the effectiveness of modules and rigs are reduced if more than one item is fitted on a ship which effects the same statistic. For instance if a module or rig grants a 10% boost to a ships velocity and another module or rig which grants 5% boost to the ships are both fitted, the ship will not receive a 15% boost to the velocity. Because both these items effect velocity their effectiveness is reduced. The more items that effect the same ships attribute that are fitted the less effect they will have overall. Typically fitting more than three modules that affects the same statistic brings little benefit.
Its also important to note that the sequence the modules are fitted to the ship do not determine how effective they are. The stacking penalty will be calculated based on the highest modifier granting its full bonus, then the second highest will receive a small penalty, the third strongest module receiving a higher penalty than the second and so on.This is reflected in the table below:
First: 100% effective
Second: 86.9% effective
Third: 57.1% effective
Fourth: 28.3% effective
Fifth: 10.6% effective
Typically any items that is effected will have the following message in their information window:
'Penalty: Using more than one type of this module or similar modules that affect the same attribute on the ship will be penalized.'
Items which grant an absolute bonus (such as +1 Warp Strength or 15KM Drone Control Range) are not effected by stacking penalties. Typically only modules or rigs that grant a percentage bonus or penalty are effected.