I'm not going to get into AH vs. real life performance. I haven't done any testing and I have faith that the HTC guys want weapons performance to be accurate.
1. MG 151 series were electrically fired, and thus very reliable. More reliable than the Hispano. I'm not saying the Hispano was unreliable mind you.
Reliability isn't modeled by HTC (yet?), so this real life point is 'moot'.
2. I don't believe (but I do not know either) that HTC has taken the time to model different types of ammunition per round. Makes sense if they haven't - they've been working on other things. I get the feeling that the cannon rounds are a little 'abstracted' (I have no problem with this - when the issue is addressed I bet it will be addressed top to bottom and done right).
The MG 151/20 (and most other fighter weapons) would be more effective overall if players could choose loadouts...i.e. 1 of 5 or 6 different types of loadouts. If you were expecting to be fighting enemy fighters, you'd load what the LW did in real life - mostly AP and API (and from '44 onward some APHE) - higher velocity rounds with a better ballistic coefficient than the pure HE and HEI used vs. bombers. Or you'd have 1 HE or HEI per 5, so if you got in close you'd tear a fighter up, but 80% of your rounds were still accurate and kept good hitting power at range. Hooligan did a study once that was dead on - hit a fighter with something powerful and you are going to mess it up. There's not enough room in a fighter for lots of 'dead air hits don't matter' space. You don't need big 2cm HE rounds to kill a Spitfire or Mustang. 1 2cm AP and 1 2cm API will probably do the trick if you hit center mass from the stern.
The Hispano most likely has AP ballistics with a little more killing power to simulate some HE rounds. But the Hispano was AP only until some time after 1942 (I think it was late 1943, some RAF expert could probably easily get an exact date).
In other words, for the first half of the war the Hispano was a big very powerful .50 that overpenetrated. Deadly, but not as '1 hit' deadly when not hitting center mass as a Hispano firing a mixture of AP and HE (i.e. a 2cm Hispano HE round hitting a wing spar near the tip of a wing could blow 3' of wingtip off sometimes, whereas a 2cm Hispano AP round would almost never do this - losing 3' of wingtip at least makes you a mission kill...except in the AH MA ehehhe).
3. MG 151/20 was lighter than Hispano. Not as long a range, not as accurate at longer ranges, but you could put 2 on a fighter instead of 1 Hispano in terms of weight, etc. (talking about earlier Hispanos here). And the most important thing to remember...
99% of the players in AH have more 'thru the sight in flight' gunnery time than your average WW2 pilot did. Worrying about weather or not your pilot had super accurate cannons at 800 yds. when he only had 2 cannons in his wing roots - why worry about this? 1% of your pilots (probably less) were going have any chance of hitting an enemy fighter at 800 yds. with those 2 cannons. The numbers escape me but close to 50% (or more) of the air to air kills in WW2 were surprise attacks weren't they (i.e. Saburo Jones is looking at 1 F6F when another F6F he doesn't see lights him up). If your gun package could score lethal hits at 300 meters you had no worries in most cases. And as the war advanced - you didn't have 'riding the stall knife fights in the vertical between a P-47 and a Bf 109' from 1944 onward in real life. Make 2 passes. If the 109 lost 4000' of altitude he wasn't a threat to the bombers. If the P-47 lost 4000' he wasn't going to bounce the Fw 190A-8s before they could reach the B-17s. Why stay for the kill? Your wingmen are up above and you still have a mission to fly.
As the war went on - you zoom in, make a couple of gun passes, and get the hell out. You may take the Bf 109 in the knife fight. The odds of being caught by another 109 after you 'won', when you had no speed left, were too high.
.50 MGs are a different story. Fighting vs. A6Ms, with 6 or 8 .50s and a shotgun pattern convergance, where a single API hit can damage 2 or 3 critical systems on an A6M (pilot, fuel, etc.)...well then fanning at an A6M at 700 yds. with 6 or 8 .50 MGs makes some sense.
The point is moot. The damage model could be better. You take HTCs track record of improvements and it will be made better some day (as in 3 HE hits on a wing gives you some added drag for the rest of the mission, etc. - even if the wing itself doesn't critically fail).
When the damage model is revamped, the ammunition and ballistics, etc. will probably be done at the same time. You have to remember that the FM of AH in general might not be able to handle this yet. It might take some major coding. This was the reason you didn't have the effects of a 'lifting body' in WB, or so I heard - the base FM wasn't set up to do it right.
What you have now for gun modeling and damage modeling is the best they could give you given priorities and man hours available. That's more than most companies in this business offer in my experience. The numbers guy cares about getting the numbers right. The coder is a supergeek hard core coder. Things will be more realistic in 1 year than they are now. Don't sweat it. Remember the diference between real life WW2 air combat (especially when talking about post '42 aircraft and armament) and the AH MA.
Mike/wulfie14