I meant to relate more to RS vs airsoft instead of player "airsoft shooting" skill and required BBs.
Sure if you have amazing rifle and you are a super player you only need 2 BBs when others need 30. But if you compare capabilities of RS vs airsoft its not just the decrease in range.
Airsoft guns are less accurate overall.
It might take a couple of hits for enemy to feel the hit and call it.
You cant shoot through cover like doors and tables.
"Real cap" was derived from RS, not "player's skill" and "gun performance". Just like in real life, if you are better shot and you have a better gun you wont need as many bullets as a shitty shot with a rusted gun. If you dont care about RS comparison might as well pull numbers out of thin air.. Real cap is 27 rounds! But its not the case... And since we are comparing to RS we should look at "loss" of "destructive power" along with range and accuracy.
If you are outdoors in a field any decent shooter will hit a man size target from 100feet with a real M4. But in airsoft, because of reasons mentioned above, range, accuracy, player's ability to feel the hit, it will take you more than 1 BB to make a kill. Most likely you will spend first 5 to adjust to the wind and then 5-10 more to ensure person calls hit.
Thats how I guesstimated 10 to 1 ratio.