I'm by no means an expert on this, however, I will state what I've noticed...
.303s are just as deadly to Ostwind turrets (if not more so) than cannon rounds. Your not busting the armor...you're killing the crew.
Somewhere HT way back when, stated that the Ostwind turret would keep firing until all it's crew was killed. This implies that it is not vehicle damage, but human damage you must worry about.
With this in mind...near misses by 1000 lbs bombs are not as lethal as 10 direct hits from .303s. Those little buggers probably ricochet all around the inside of the "cookie tin" putting multiple holes in the crew. I believe that .303s have a higher rate of fire, and probably better ballistics. Therefore, you are more likely to land enough hits inside the turret with .303s than with baseball ballistic 30 mm.
If anyone wants to try this, lets go to the DA and test it out...I'm really interested in knowing what will kill an Ostwind turret.