Not that I really want to fuel another .50 caliber discussion (that has raged for almost a decade on the Zoo), but while waiting for a "constant develompment update" every thing is allowed
I found an interesting text regarding the armor protection of fighters during world war 2:
http://www.geocities.com/CapeCanaver...n/fgun-ar.html
An exerpt about penetration from .50:
"How effective was the armour? It's thickness varied from 8 mm to about 13 mm. The armour was certainly effective against rifle-calibre machineguns, but these weapons were increasingly replaced by far more powerful medium-calibre machineguns or by cannon. The American .50 AP M2 round, a projectile with a high muzzle velocity, was expected to penetrate 1 inch (24.5 mm) at 100 yards (91 mm) and the AP-I M8 round still 7/8 inch. However, such armour penetration figures are traditionally measured against a homogeneous "standard" plate, while the armour plate fitted to aircraft would be face-hardened plate of good quality, to achieve maximal protection for minimal weight. Also important was that before it could hit the armour, the projectile had to pass through the aircraft skin and maybe structural members, which would deflect it or slow it down and was likely to cause tumbling, which would considerable reduce armour penetration. In this way relatively thin plates could greatly increase the protection. Equipment in the aft fuselage could be carefully arrange so that the bullet would have to pass it first, before it could hit the pilot. Finally, typical firing distances were of the order of 300 yards. Most airforces seem to have felt that the armour of their fighters offered substantial protection against .50 and even 20 mm rounds."
/Mazex