Actually, I've witnessed such light caliber knck-outs in CM much more often than I think it happened in RL.
Many accounts speak of multiple penetrations not resulting in knock-outs or even bail-outs. At Dien Bien Phu, the french Chafee platoon survived almost through the entire battle (less one tank, which brewed up early in the siege), although in the end, they had amassed many hits, mostly from 57 and 75 mm RR. They were immobilized on several instances, abandoned and recovered, during the same battle. It would be great to be able to have the crews recover their AFV once they no longer are suppressed.
Same goes for the japanese tanks at Nomonhan (aka Khalkhin Gol). They were hit several times by 45mm rounds fired by both BT tanks and AT guns, especially in the initial stages of the battle. However, despite penetrations, they remained in the battle until attacked by heavier russian tanks (T34 and KV1) later on. The penetrating AT fire would cause them to withdraw, but without abandoning the tank when at all possible, even if some of the crews were wounded or killed. This is another feature badly missing: panicked or out-of-control tanks, withdrawing or driving to the rear. AV's in CM are almost always knocked out by penetrating hits, even with very small penetration marginal. The resilience of AV's to such hits should be more akin to the way unarmored vehicles resist to HE fire... We've all seen trucks under fire from MG's 200 metres away and not abandoned directly (although 1 or 2 rounds in every salvo fired are bound to hit the truck).
The 20 mm gun carried by various AFV's in CM is the KwK38 with a clip of 8 rounds that can be fired automatically. Given the fact that the weapon always is turret mounted (thus very stable), I would expect these 8 rounds to be fired rather quickly, maybe in one burst, if the target is close enough... The same goes for the .50's, as they can fire at very high rates of fire if the target is close enough to ensure hits without prolongued aiming (unlike now when there always are those 5-6 secondes between bursts)...