Originally posted by Heinkel 
Bf109E-4
-Are the mine rounds modeled for the MgFF cannons? In WW2OL, you see the actuall 20mm round explode in the air, creating a flak puff if it didnt detinate (make contact with enemy aircraft)
  
The puffs of smoke in WWIIOL are due to the timed fuse detonating.
I believe several/most?/many cannon rounds on both sides had a timed detonation due to two purposes: 
- incase the contact fuse didn't work (or didn't have one at all) 
- for safety, so that the cannon shells could only explode near the intended target, and not on the ground.
  There is atleast one historic occurence of a surprised target realizing that they are under attack by cannon shells exploding in mid air in front of them. I don't think that the shells were intended to explode when they are a near miss. So, this would be more of a eye candy item rather than a historic accuracy item.