I have a wild theory (which I am not going to test), that to calculate ground AA fire strength, game just divides penetration, and effect of devices by 10. When you compare those values to aircraft guns, you will discover that suddenly ground guns seems to be at least category lower, that their aircraft calibers, and it gets even worse, for larger guns.
For example 20mm Oerlikon have 15 effect, and 20 penetration (that gives 1.5, and 2), while 20mm aircraft gun have 4 effect, and 3 penetration.
To check what will happen, I changed ALL alternate values for AA, and DP guns to be TWICE their original. It is pretty easy with magic lines. Although I have no idea what first value is used for. Just copy it into alternate columns:
In theory it should be massacre (double damage!), in practice effect is barely visible in combat report, but you surely see greater loses in summary screen. But not that much greater.
I have also another wild theory, that accuracy is just value to compare with plane maneuver rating, so anything above around 20 is just helping to hit fighters, not makes AA gun any better against bombers. I would have to see what will happen to ZEROs in PH strike, with that change.
In attachment there is modifed devices file (from my Scenario 31), just change extension to dat. It should work with all Scenarios (but beta can cause unexpected consequences), which uses original data.
It also includes historical Japanese bombs (defined from slot 1770). I have used:
TM 9-1985-4/TO 39B-1A-11 "Japanese explosive ordnance", and
O-23 "Japanese Naval Bombs"
Overall, Japanes bombs are close (+- 10%) to original database, but there are few exceptions:
1) Japan only had TWO real AP bombs. 500 kg, and 800 kg (used in PH). There is 250kg model, with small booster (later removed, because bomb shattered), but it had quite large explosive charge (over 20%). So anything called SAP is just GP bomb, with minimally better penetration.
2) Penetration is genarally low
3) 800 kg bombs are pretty common (but not that AP type used at PH)
4) Navy had not used any 100 kg bombs (and that creates several problems for Navy planes)
5) I have not included several types of 250kg anti-airstrip bombs, as the only different value, I could think of, was better accuracy, and I am not even sure it is used in ground attacks