The rifle sized mg's in AH is grossly undermodeled compared to the .50 cal. class weapons. This I think is in part due to to the simplistic damage model. Do I think 30 rounds of .30 cal would rip a wing of? No ... not even on a zeke. I have seen some 190's loose a wing due to ammo explosion, and a lot of flaming zekes (their main weakness was lack of self-sealing fuel tanks), but I have rarely seen planes loose major components like a wing to mg or hmg fire. Somtimes with cannon fire.
AH models absolute damage to all structural components AFAIK, meaning the component (wing in this case) doesn't loose integrity gradually like in RL, but continues to be just as strong untill it is damaged beyond it set limit ... and then fails completely. Those few guncam films where I have seen wing failure like this were in either high G load turnfights or high speed tailshots, where the stress of G or aerodynamic force ripped the weakened wing off.
A .50 cal. round do not do much more damage to a structure like a wing than a .30 cal. round. This is because both rounds have sufficient kinetic energy to penetrate and completely pass through the structure, even a heavy aluminum wing spar. The .50 cal is of course much more powerful, but it has no way of transfering all that kinetic energy to structural damage. A human being has the consistency of jello. The reason why a rifle round does more damage than a pistol round is because the higher kinetic energy of the rifle round causes more hydro shock in the human body (like shooting a baloon filled with water). Against a sheet of aluminum both rounds would do much the same damage if they both penetrated, the rifle bullet will just fly farther off into the woods. As Rshubert found out the .45 cal. pistol round actually did more damage to the sheet/structure by not penetrating because it was thus capable of transfering all it's energy to the target rather than just punching a small hole.
The reason the .50 cal. round was better at shooting down planes has nothing to do with the structure of the planes. The .50 cal. was more effective at causing critical component damage. At good angles the a .50 AP(I) round will crack the engine block, penetrate cockpit armor, the higher kinetic energy has a greater chance of rupturing self-sealing fuel tanks due to increased hydro shock, the projectile is bigger and thus capable of carrying more incendiary chemical power which increases the chanse of setting fire to fuel, hot engine oil and some hydraulic fluids.
Aluminum is a very good material to use in lightweigth loadbearing structures, but it is soft and suceptible to damage. The MG3 is chamered for the 7.62x51mm NATO round, which is somewhat less powerfull than the 7.92x57mm Mauser or the .303 British (7.7×56mm). The M113 APC has more than 1.5 inch hardened aluminum side armor which is sufficient to stop rifle sized ball rounds at all but the shortest ranges. I have personally shot a 50 round belt of AP at the side of a M113 at 400 meters (437 yards), not one round glanced off or failed to penetrate, and they did some impressive damage bouncing around the interior. So a .30 will penetrate the wing spar of an F4U. Would 30 rounds rip a wing off? nope. Will 30 .50 cal. rounds rip a wing off? nope. Will 30 HE cannon rounds rip a wing of? yes, probably.
My .2 cal... err, $
