I didn't think the loadout changes were working in quick missions.

I watched once the top gunner got sprayed with bullets, and he didn't get hurt, but bottom gunner or even bombardier seemed dead after this. (could be one or both was dead before this, but seem strange)

.303 B MkIV incendiary is the Dixon/De Wildes.

As far as I can recall, there were no HE .303 rounds. Dixon/De Wilde rounds were incendiary.

Thanks for all the advice here! I actually fire at 150 yards just like my convergence, but I'm for sure going to try a mix of incendiary and AP at the wing root!

And for sure there are many records of pilots emptying all their ammo with no result, at the other hand there are a lot of "I fired a short burst and saw the left landing gear falling down" etc.... Never happens to me ;)

Then of course the Polish head on is attractive :) Will try that too. This sim has so much potential now that the fps is decent. Eagerly awaiting my 2600k / GTX580 rig to throw some hardware at the problem also!

I seem to get the best results with loading with incendiary tracers, rest all AP with 2 guns fitted with De Wilde @150m conv. So ok then :D half AP/ half incendiary. However, I do feel a bit annoyed about the whole .303 effect on the planes.
For 1 everyone states that if you sit on the six of say a Me 109 and fire that there is nothing of importance in the tail and everything gets blocked by the armour behind the seat of the pilot. Firstly, so what then of the AP rounds? Are they not supposed to pass straight through the armour, the fuel tanks the pilot and hit the engine? X4 in my case. I thing all of the default load outs have at least 1 AP load. Isn’t the tail also considered to be of some importance?
Secondly, everyone then states that the .303 is so ineffective. I guess if you shoot the plane with 1 bullet, then yes in retrospect the effects could be minimal. However, you have 8 very high rate of fire guns firing all at once. The effect on the plane would by more like ripping paper than punching a hundred wholes into it one at a time with a couple of seconds in between.
In combat, planes losing their wings were more an effect of being torn off due to the sudden force of the bullet impact and the fact that the wing is already under strain from the wind flow rather than the struts being individually severed by bullet fire. If you see the amount of cartridges that come out of a fellow Hurri firing, it seems it would be more effective to just fly in front of the enemy plane and have it banged up by the incoming cartridges :)
BUT.... the last mission in the British campaign: Seeing tracers fly out in the night sky to the enemy plane, the glow of bullet impacts, then the ensuing fire and fire ball upon crashing .... Amazing!

Nothing wrong with the guns, just have to learn how to use them! All my flying for the last few days has been practice against bombers. With the ammo loadout described in the above post set at 150 you can knock anything out of the sky with the rotol.

Even sitting on six of a Heinkel or Dornier (when you've got the gunner) works well if you land enough hits. I've ripped the entire tail off several times and getting the elevator is also good news.

Jip, if I don't fly straight into the 111's straight on (dope), I can usually take out about 3 before my ammo runs out with the above mentioned loadout.
When chasing 111's, they aren't really that slow, so I can understand getting stuck behind their sixes. I usually try to start my attack from a bit above, but I rarely get a fatal hit in the few seconds until I'm right behind the bomber. In that case, wait till you are at your convergence setting (at 150m I can start to see the components I want to hit) away and try to aim for the engines in the wings (which is not all that easy from straight behind.... the tail is somewhat in the way). Some might hit the aileron and some might hit the fuel tank though, so it’s a good area to aim. Try not to fire blindly(usually into the tail) if you get too close, rather wait till you're slow enough to maintain the 150m distance or go around for a second pass). I also just read in the IL 46 plane guide that the plane should be able to fly with only one engine operational, so you’ll have to target both theoretically. Try to use your sidewinders only if need be.

The AP rounds were designed for Infantry use. The main reason they are so rubbish against aircraft armour is that they had to hit the armour tip first. The superstructure of the aircraft would 'tumble' the bullets making them spin end over end. The chances of the armour being penetrated were very, very small.

They were designed to be fired directly at armour (tanks etc).

The 8 x .303 should be a good 109 killer because all the vital parts are contained within a much smaller space. (stating the obvious!)