wasnt there some plane that the firing of there cannons made it stop or slow down from the force..
Quite a few, actually. It was also said that the early model B52's actually gained a few knots of speed when the rear gunner (20mm?) fired for any amount of time. Take it for what it is worth.

In regards to the IL-2's accuracy, even the Hurricare IID hasa bit of a jolt when firing. Nothing to really make it less accurate, but it is far more noticable than when firing the IL-2 much faster firing 37mm.
Does anyone have pics of the Soviet 37mm and British 40mm shells? I'm curious as to how they compare in case size. IIRC, the British 40mm was a naval gun that fired an HE warhead and the IL-2 fired an AP projectile, yes?