Regarding how lethal the guns can/should be...
(paraphrased from Air Classics Magazine, Feb. 2000)
Hans Joachim Marseille, flying with JG52 over France between 1939 and 1941, and with JG27 over North Africa between the spring of 1941 and Sept. 30 of 1942, scored a total of 158 kills in 382 missions, with one 17 kill day, and averaging approximately 15 rounds fired per kill. On Sept. 1, 1942, the 17 kill day, on his first sortie before refueling he shot down 4 P-40 Kittyhawks in his BF109F, using only 20 rds. of cannon and 60 rds. of machine gun ammunition.
There are other accounts (as mentioned above) of aircraft being shredded, and still returning to base. Much of this depended on the plane in question, as several had outstanding durability records. Draw your own conclusions from this info, but with the possible exception of the F4U-1C, I think the guns are modeled pretty accurately in AH, or at least they are modeled fairly evenly across the board, with the one exception I suggested.