I fly mostly online and can almost swear that when I'm flying in certain aircraft I can get hit once and the blooming thing feels like its made of tinfoil and just fails apart. Invariably I get taken down an awful lot from being 1 shot pilot killed (particularly flying in the 190). However, when I'm the one shooting back, I can convince myself that the enemy aircraft (Allied or Lufty) is soaking up tons of damage
With regard to the P-47, having flown in it and also shot at it a fair few times purely from a personal view point in seems to soak up MG fire fairly well but it can't take too many Mk 108 hits and indeed should it, or any of the current aircraft, considering it's a bomber killer round?
I personally think that the most effective gun platform currently is the P-51. it just seems to swat enemy aircraft down with relative ease.