There are crackshots and there are bad shots, but frankly, shooting down something outside of 1500 yards in AH, with the Ostwind, is more or less luck.
It's simply and undeniably rests on the "spray as much lead as you can into the air, and hope something hits" basis. Learning to lead the aiming reticle does help, but even if the lead is good, you have to pray that the enemy plane doesn't fly in between the wall of tracers, since the firing rate is so slow.
Usually, the only time Osties ever shoot down something besides out of luck, is when an enemy jabo heads straight towards it, lobbing rockets and bombs. It usually kills both of the antagonists, the Ostie knocking off a wing or fuselage, and the plane vaporizing the flak wagon.
The real value of Osties in field defense, is that it's a psychological weapon.
When multiple Osties are scattered round the field, even the most daring pilot hesitates to attack that field. Unless the enemies come in with a humongous suicidal numbers advantage, usually they will choose to stay away from the field, which gives some valuable time for defending fighters to up and organize a quick defense.
And if the attackers decide to clean the field up and really suppress the field, the Osties make sure it drags a lot of attacking planes to the tomb - inevitably making the attacking force weaker. (That's because the furball stupidity usually prevents the attackers from bringing ordnance.)
